Magnetic tape apparatus

ABSTRACT

A magnetic tape apparatus, in which full widths at half maximum of spacing distribution measured by optical interferometry regarding a surface of a magnetic layer before and after performing a vacuum heating with respect to the magnetic tape are greater than 0 nm and equal to or smaller than 15.0 nm, a difference between spacings measured by optical interferometry regarding the surface of the magnetic layer before and after performing the vacuum heating is greater than 0 nm and equal to or smaller than 12.0 nm, and the extraction unit performs a waveform equalization process according to a deviation amount between positions of the magnetic tape and the reading element unit, with respect to each reading result for each reading element, to extract data derived from the reading target track from the reading result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2018-125570 filed on Jun. 29, 2018 and Japanese PatentApplication No. 2019-100043 filed on May 29, 2019. Each of the aboveapplications is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape apparatus.

2. Description of the Related Art

A magnetic recording and reproducing apparatus which performs recordingof data on a magnetic recording medium and/or reading (reproducing) ofthe recorded data is widely divided into a magnetic disk apparatus and amagnetic tape apparatus. A representative example of the magnetic diskapparatus is a hard disk drive (HDD). In the magnetic disk apparatus, amagnetic disk is used as the magnetic recording medium. Meanwhile, inthe magnetic tape apparatus, a magnetic tape is used as the magneticrecording medium.

In both of the magnetic disk apparatus and the magnetic tape apparatus,it is preferable to narrow a recording track width, in order to increaserecording capacity (increase capacity). However, the recording trackwidth is narrowed, a signal of an adjacent track is easily mixed with asignal of a reading target track during the reproducing, andaccordingly, it is difficult to maintain reproducing quality such as asignal-to-noise ratio (SNR). In regard to this point, in recent years,it is proposed to improve reproducing quality by reading a signal of arecording track by a plurality of reading elements (also referred to as“reproducing elements”) two-dimensionally (for example, seeJP2016-110680A, JP2011-134372A, and U.S. Pat. No. 7,755,863B). In a casewhere the reproducing quality can be improved by doing so, thereproducing quality can be maintained, even in a case where therecording track width is narrowed, and accordingly, it is possible toincrease recording capacity by narrowing the recording track width.

SUMMARY OF THE INVENTION

In JP2016-110680A and JP2011-134372A, studies regarding a magnetic diskapparatus are conducted. Meanwhile, in recent years, a magnetic tape isreceiving attention as a data storage medium for storing a large contentof data for a long period of time. However, the magnetic tape apparatusis a sliding type apparatus in which data reading (reproducing) isperformed due to a contact and sliding between the magnetic tape and areading element. Accordingly, a relational position between the readingelement and a reading target track easily changes during thereproducing, and the reproducing quality tends to be hardly improved,compared to a magnetic disk apparatus. U.S. Pat. No. 7,755,863Bdiscloses the description regarding the magnetic tape apparatus (tapedrive), but does not disclose specific means for improving thereproducing quality of the magnetic tape apparatus.

One aspect of the invention provides a magnetic tape apparatus capableof improving the reproducing quality.

According to one aspect of the invention, there is provided a magnetictape apparatus comprising: a magnetic tape; a reading element unit; andan extraction unit, in which the magnetic tape includes a non-magneticsupport, and a magnetic layer including a ferromagnetic powder, abinding agent, and fatty acid ester on the non-magnetic support, a fullwidth at half maximum of spacing distribution measured by opticalinterferometry regarding a surface of the magnetic layer beforeperforming a vacuum heating with respect to the magnetic tape(hereinafter, also referred to as “FWHM_(before)”) is greater than 0 nmand equal to or smaller than 15.0 nm, a full width at half maximum ofspacing distribution measured by optical interferometry regarding thesurface of the magnetic layer after performing the vacuum heating withrespect to the magnetic tape (hereinafter, also referred to as“FWHM_(after)”) is greater than 0 nm and equal to or smaller than 15.0nm, a difference (S_(after)−S_(before)) between a spacing S_(after)measured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the magnetic layer before performing the vacuumheating with respect to the magnetic tape (hereinafter, also simplyreferred to as a “difference (S_(after)−S_(before))^(”)) is greater than0 nm and equal to or smaller than 12.0 nm, the reading element unitincludes a plurality of reading elements each of which reads data by alinear scanning method from a specific track region including a readingtarget track in a track region included in the magnetic tape, and theextraction unit performs a waveform equalization process according to adeviation amount between positions of the magnetic tape and the readingelement unit, with respect to each reading result for each readingelement, to extract data derived from the reading target track from thereading result.

In one aspect, parts of the plurality of reading elements may beoverlapped each other in a running direction of the magnetic tape.

In one aspect, the specific track region may be a region including thereading target track and adjacent tracks which are adjacent to thereading target track, and each of the plurality of reading elements maystraddle over both of the reading target track and the adjacent track,in a case where a positional relationship with the magnetic tape ischanged.

In one aspect, the plurality of reading elements may be disposed in aline in a state of being adjacent to each other, in a width direction ofthe magnetic tape.

In one aspect, the plurality of reading elements may fall in the readingtarget track in a width direction of the magnetic tape.

In one aspect, the waveform equalization process may be performed byusing a tap coefficient determined in accordance with the deviationamount.

In one aspect, regarding each of the plurality of reading elements, aratio between an overlapping region with the reading target track and anoverlapping region with an adjacent track which is adjacent to thereading target track may be specified from the deviation amount, and thetap coefficient may be determined in accordance with the specifiedratio.

In one aspect, the deviation amount may be determined in accordance witha result obtained by reading a servo pattern applied to the magnetictape in advance, by a servo element.

In one aspect, a reading operation by the reading element unit may beperformed synchronously with a reading operation by the servo element.

In one aspect, the extraction unit may include a two-dimensional finiteimpulse response (FIR) filter, and the two-dimensional FIR filter maycompose each result obtained by performing the waveform equalizationprocess with respect to each reading result for each reading element, toextract data derived from the reading target track from the readingresult.

In one aspect, the plurality of reading elements may be a pair ofreading elements.

In one aspect, the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the magneticlayer before performing the vacuum heating with respect to the magnetictape may be 2.0 nm to 15.0 nm.

In one aspect, the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape may be 2.0 nm to 15.0 nm.

In one aspect, the difference (S_(after)−S_(before)) may be 1.0 nm to12.0 nm.

According to one aspect of the invention, it is possible to provide amagnetic tape apparatus capable of reproducing data recorded on amagnetic tape with high reproducing quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view showing an example of theentire configuration of a magnetic tape apparatus.

FIG. 2 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading head and a magnetic tapeincluded in the magnetic tape apparatus.

FIG. 3 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading element unit and a magnetictape.

FIG. 4 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a track region and a reading elementpair.

FIG. 5 is a graph showing an example of a correlation between an SNRregarding each of a single reading element data item and a firstcomposite data item under a first condition, and track off-set.

FIG. 6 is a graph showing an example of a correlation between an SNRregarding each of the single reading element data item and a secondcomposite data item under a second condition, and track off-set.

FIG. 7 is a block view showing an example of a main configuration ofhardware of an electric system of the magnetic tape apparatus.

FIG. 8 is a conceptual view provided for description of a method ofcalculating a deviation amount.

FIG. 9 is a flowchart showing an example of a flow of a magnetic tapereading process.

FIG. 10 is a conceptual view provided for description of a processperformed by a two-dimensional FIR filter of an extraction unit.

FIG. 11 is a schematic plan view showing an example of a state where thereading element unit straddles over a reading target track and a secondnoise mixing source track.

FIG. 12 is a schematic plan view showing a first modification example ofthe reading element unit.

FIG. 13 is a schematic plan view showing a second modification exampleof the reading element unit.

FIG. 14 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

FIG. 15 is a schematic configuration view of a vibration impartingdevice used in examples.

FIG. 16 is a conceptual view provided for description of a first exampleof the related art.

FIG. 17 is a conceptual view provided for description of a secondexample of the related art.

FIG. 18 is a view showing an example of a two-dimensional image of areproducing signal obtained from a single reading element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A magnetic tape apparatus according to one aspect of the inventionincludes a magnetic tape, a reading element unit, and an extractionunit.

Regarding the reading of data from the magnetic tape, in the example ofthe related art shown in FIG. 16, an elongated reading head 200comprises a plurality of reading elements 202 along a longitudinaldirection. In a magnetic tape 204, a plurality of tracks 206 are formed.The reading head 200 is disposed so that the longitudinal directioncoincides with a width direction of the magnetic tape 204. In addition,each of the plurality of reading elements 202 is allocated for each ofthe plurality of tracks 206 in a one-to-one relation, and reads datafrom the track 206 at a position faced.

However, in general, the magnetic tape 204 expands and contracts due totime elapse, an environment, a change of a tension, and the like. In acase where the magnetic tape expands and contracts in a width directionof the magnetic tape 204, the center of the reading element 202 disposedon both end in the longitudinal direction in the reading head 200 isdeviated from the center of the track 206. In a case where the magnetictape 204 is modified due to the expansion and contraction in a widthdirection, particularly, the reading elements 202 closer to both end ofthe reading head 200, among the plurality of reading elements 202,receive a greater effect of off-track. In order to reduce the effect ofthe off-track, for example, a method of applying a surplus width to thewidth of the track 206 has been considered. However, as the width of thetrack 206 increases, a recording capacity of the magnetic tape 204decreases.

In addition, as shown in the example of the related art shown in FIG.17, in general, a servo element 208 is provided in the reading head 200.A servo pattern which is applied to the magnetic tape 204 in advancealong a running direction of the magnetic tape 204 is read by the servoelement 208. A control device (not shown) specifies that which positionon the magnetic tape 204 the reading element 202 runs on, for example,at regular time interval, from the servo signal obtained by reading theservo pattern by the servo element 208. Accordingly, a position errorsignal (PES) in a width direction of the magnetic tape 204 is detectedby the control device.

As described above, in a case where the control device specifies therunning position of the reading element 202, a feedback control isperformed with respect to an actuator (not shown) for the reading headby the control device based on the specified running position, andaccordingly, the tracking of the magnetic tape 204 in the widthdirection is realized.

However, although the tracking is performed, sharp vibration, a highfrequency component of jitter, and the like are factors of an increasein PES, and this causes a deterioration in reproducing quality of dataread from a reading target track.

On the other hand, in the magnetic tape apparatus according to oneaspect of the invention, the reading element unit includes a pluralityof reading elements each of which reads data by a linear scanning methodfrom a specific track region including a reading target track in a trackregion included in the magnetic tape. The extraction unit performs awaveform equalization process according to a deviation amount betweenpositions of the magnetic tape and the reading element unit, withrespect to each reading result for each reading element, to extract dataderived from the reading target track from the reading result.Therefore, according to the magnetic tape apparatus, it is possible toincrease the reproducing quality of data read from the reading targettrack, compared to a case where data is read only by a single readingelement from the reading target track by a linear scanning method. As aresult, it is possible to increase an acceptable amount of the deviationamount (track off-set amount) capable of ensuring excellent reproducingquality.

In addition, the deviation amount is generally detected by the readingof the servo pattern. However, in practice, the positional change mayoccur on a cycle shorter than a cycle on which the servo pattern isformed. With respect to the reading result obtained by reading at aportion where the positional change on such a short cycle occurs, thewaveform equalization process according to the deviation amount may notbe always the optimal waveform equalization process. With respect tothis, in a case where the positional change on such a short cycle can beprevented, more suitable waveform equalization process can be performedwith respect to the reading result obtained by reading at each portion.As a result, it is possible to increase the acceptable amount of thedeviation amount capable of ensuring excellent reproducing quality bythe waveform equalization process.

As described above, an increase in acceptable amount of the deviationamount capable of ensuring excellent reproducing quality can contributeto the reproducing with high reproducing quality (for example, high SNRor low error rate), even in a case where a track margin (recording trackwidth−reproducing element width) is decreased. A decrease in trackmargin can contribute to an increase in number of recording trackscapable of being disposed in a width direction of the magnetic tape bydecreasing the recording track width, that is, realization of highcapacity.

With respect to the point described above, it is considered that theFWHM_(before), the FWHM_(after), and the difference(S_(after)−S_(before)) in the ranges described above of the magnetictape which performs the reading of data in the magnetic tape apparatus,contributes to improvement of sliding properties between the readingelement and the magnetic tape, while preventing occurrence of stickingbetween the magnetic tape and the reading element. It is surmised thatthis contributes to prevention of the positional change on the shortcycle. This point will be further described later.

Hereinafter, the magnetic tape apparatus will be described later indetail. Hereinafter, the magnetic tape apparatus may be described withreference to the drawings. However, the magnetic tape apparatus is notlimited to the aspect shown in the drawings.

Configuration of Magnetic Tape Apparatus and Magnetic Tape ReadingProcess

As an example shown in FIG. 1, a magnetic tape apparatus 10 comprises amagnetic tape cartridge 12, a transportation device 14, a reading head16, and a control device 18.

The magnetic tape apparatus 10 is an apparatus which extracts a magnetictape MT from the magnetic tape cartridge 12 and reads data from theextracted magnetic tape MT by using the reading head 16 by a linearscanning method. The reading of data can also be referred to asreproducing of data.

The control device 18 controls the entire magnetic tape apparatus 10. Inone aspect, the control performed by the control device 18 can berealized with an application specific integrated circuit (ASIC). Inaddition, in one aspect, the control performed by the control device 18can be realized with a field-programmable gate array (FPGA). The controlperformed by the control device 18 may be realized with a computerincluding a central processing unit (CPU), a read only memory (ROM), anda random access memory (RAM). Further, the control may be realized witha combination of two or more of AISC, FPGA, and the computer.

The transportation device 14 is a device which selectively transportsthe magnetic tape MT in a forward direction and a backward direction,and comprises a sending motor 20, a winding reel 22, a winding motor 24,a plurality of guide rollers GR, and the control device 18.

A cartridge reel CR is provided in the magnetic tape cartridge 12. Themagnetic tape MT is wound around the cartridge reel CR. The sendingmotor 20 causes the cartridge reel CR in the magnetic tape cartridge 12to be rotatably driven under the control of the control device 18. Thecontrol device 18 controls the sending motor 20 to control a rotationdirection, a rotation rate, a rotation torque, and the like of thecartridge reel CR.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the sending motor 20 so that the magnetictape MT runs in a forward direction. The rotation rate, the rotationtorque, and the like of the sending motor 20 are adjusted in accordancewith a speed of the magnetic tape MT wound around the winding reel 22.

The winding motor 24 causes the winding reel 22 to be rotatably drivenunder the control of the control device 18. The control device 18controls the winding motor 24 to control a rotation direction, arotation rate, a rotation torque, and the like of the winding reel 22.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the winding motor 24 so that the magnetictape MT runs in the forward direction. The rotation rate, the rotationtorque, and the like of the winding motor 24 are adjusted in accordancewith a speed of the magnetic tape MT wound around the winding reel 22.

By adjusting the rotation rate, the rotation torque, and the like ofeach of the sending motor 20 and the winding motor 24 as describedabove, a tension in a predetermined range is applied to the magnetictape MT. Here, the predetermined range indicates a range of a tensionobtained from a computer simulation and/or a test performed with a realmachine, as a range of a tension in which data can be read from themagnetic tape MT by the reading head 16, for example.

In a case of rewinding the magnetic tape MT to the cartridge reel CR,the control device 18 rotates the sending motor 20 and the winding motor24 so that the magnetic tape MT runs in the backward direction.

In one aspect, the tension of the magnetic tape MT is controlled bycontrolling the rotation rate, the rotation torque, and the like of thesending motor 20 and the winding motor 24. In addition, in one aspect,the tension of the magnetic tape MT may be controlled by using a dancerroller, or may be controlled by drawing the magnetic tape MT to a vacuumchamber.

Each of the plurality of guide rollers GR is a roller guiding themagnetic tape MT. A running path of the magnetic tape MT is determinedby separately disposing the plurality of guide rollers GR on positionscrossing the reading head 16 between the magnetic tape cartridge 12 andthe winding reel 22.

The reading head 16 comprises a reading unit 26 and a holder 28. Thereading unit 26 is held by the holder 28 so as to come into contact withthe magnetic tape MT during the running.

As an example shown in FIG. 2, the magnetic tape MT comprises a trackregion 30 and a servo pattern 32. The servo pattern 32 is a pattern usedfor detection of the position of the reading head 16 on the magnetictape MT. The servo pattern 32 is a pattern in which a first diagonalline 32A at a first predetermined angle (for example, 95 degrees) and asecond diagonal line 32B at a second predetermined angle (for example,85 degrees) are alternately disposed on both end portions in a tapewidth direction at a constant pitch (cycle) along a running direction ofthe magnetic tape MT. The “tape width direction” here indicates a widthdirection of the magnetic tape MT.

The track region 30 is a region where the data which is a reading targetis written, and is formed on the center of the magnetic tape MT in thetape width direction. The “center in the tape width direction” hereindicates, for example, a region between the servo pattern 32 on one endportion and the servo pattern 32 on the other end portion of themagnetic tape MT in the tape width direction. Hereinafter, forconvenience of description, the “running direction of the magnetic tapeMT” is simply referred to as the “running direction”.

The reading unit 26 comprises a servo element pair 36 and a plurality ofreading element units 38. The holder 28 is formed to be elongated in thetape width direction, and a total length of the holder 28 in thelongitudinal direction is longer than the width of the magnetic tape MT.The servo element pair 36 are disposed on both end portions of theholder 28 in the longitudinal direction, and the plurality of readingelement units 38 are disposed on the center of the holder 28 in thelongitudinal direction.

The servo element pair 36 comprise servo elements 36A and 36B. The servoelement 36A is disposed on a position facing the servo pattern 32 on oneend portion of the magnetic tape MT in the tape width direction, and theservo element 36B is disposed on a position facing the servo pattern 32on the other end portion of the magnetic tape MT in the tape widthdirection.

In the holder 28, the plurality of reading element units 38 are disposedbetween the servo element 36A and the servo element 36B along the tapewidth direction. The track region 30 comprises the plurality of tracksat regular interval in the tape width direction, and in a default stateof the magnetic tape apparatus 10, each of the plurality of readingelement units 38 is disposed to face each track in the track region 30.

Thus, since the reading unit 26 and the magnetic tape MT relatively movelinearly along the longitudinal direction of the magnetic tape MT, thedata of each track in the track region 30 is read by each readingelement unit 38 at the corresponding position among the plurality ofreading element units 38 by the linear scanning method. In addition, inthe linear scanning method, the servo patterns 32 are read by the servoelement pair 36 synchronously with the reading operation of the readingelement units 38. That is, in one aspect of the linear scanning method,the reading with respect to the magnetic tape MT is performed inparallel by the plurality of reading element units 38 and the servoelement pair 36.

Here, “each track in the track region 30” here indicates a trackincluded in “each of a plurality of specific track region including eachreading target track in the track region included in the magnetic tape”.

The “default state of the magnetic tape apparatus 10” indicates a statewhere the magnetic tape MT is not deformed and a positional relationshipbetween the magnetic tape MT head the reading head 16 is a correctpositional relationship. Here, the “correct positional relationship”indicates a positional relationship in which the center of the magnetictape MT in the tape width direction and the center of the reading head16 in the longitudinal direction coincide with each other.

In one aspect, each of the plurality of reading element unit 38 has thesame configuration. Hereinafter, the description will be performed usingone of the plurality of reading element unit 38 as an example, forconvenience of description. As an example shown in FIG. 3, the readingelement unit 38 comprises one pair of reading elements. In the exampleshown in FIG. 3, “one pair of reading elements” indicate a first readingelement 40 and a second reading element 42. Each of the first readingelement 40 and the second reading element 42 reads data from a specifictrack region 31 including a reading target track 30A in the track region30.

In the example shown in FIG. 3, for convenience of description, onespecific track region 31 is shown. In practice, in general, in the trackregion 30, a plurality of specific track regions 31 are present, and thereading target track 30A is included in each specific track region 31.The reading element unit 38 is allocated to each of the plurality ofspecific track regions 31 in a one-to-one manner. Specifically, thereading element unit 38 is allocated to the reading target track 30A ineach of the plurality of specific track regions 31 in a one-to-onemanner.

The specific track region 31 indicates three adjacent tracks. A firsttrack among the three adjacent tracks is the reading target track 30A inthe track region 30. A second track among the three adjacent tracks is afirst noise mixing source track 30B which is one adjacent track adjacentto the reading target track 30A. A third track among the three adjacenttracks is a second noise mixing source track 30C which is one adjacenttrack adjacent to the reading target track 30A. The reading target track30A is a track at a position facing the reading element unit 38 in thetrack region 30. That is, the reading target track 30A indicates a trackhaving data to be read by the reading element unit 38.

The first noise mixing source track 30B is a track which is adjacent tothe reading target track 30A on one side in the tape width direction andis a mixing source of noise mixed to data read from the reading targettrack 30A. The second noise mixing source track 30C is a track which isadjacent to the reading target track 30A on the other side in the tapewidth direction and is a mixing source of noise mixed to data read fromthe reading target track 30A. Hereinafter, for convenience ofdescription, in a case where it is not necessary to describe the firstnoise mixing source track 30B and the second noise mixing source track30C separately, these are referred to as the “adjacent track” withoutreference numerals.

In one aspect, in the track region 30, the plurality of specific trackregions 31 are disposed at regular interval in the tape width direction.For example, in the track region 30, 32 specific track regions 31 aredisposed at regular interval in the tape width direction, and thereading element unit 38 is allocated to each specific track region 31 ina one-to-one manner.

The first reading element 40 and the second reading element 42 aredisposed at positions a part of which is overlapped in the runningdirection, in a state of being adjacent in the running direction. In adefault state of the magnetic tape apparatus 10, the first readingelement 40 is disposed at a position straddling over the reading targettrack 30A and the first noise mixing source track 30B. In a defaultstate of the magnetic tape apparatus 10, the second reading element 42is disposed at a position straddling over the reading target track 30Aand the first noise mixing source track 30B.

In a default state of the magnetic tape apparatus 10, the area of aportion of the first reading element 40 facing the reading target track30A is greater than the area of a portion of the first reading element40 facing the first noise mixing source track 30B, in a plan view.Meanwhile, in a default state of the magnetic tape apparatus 10, thearea of a portion of the second reading element 42 facing the firstnoise mixing source track 30B is greater than the area of a portion ofthe first reading element 40 facing the reading target track 30A, in aplan view.

The data read by the first reading element 40 is subjected to a waveformequalization process by a first equalizer 70 (see FIG. 7). The data readby the second reading element 42 is subjected to a waveform equalizationprocess by a second equalizer 72 (see FIG. 7). Each data item obtainedby performing the waveform equalization process by each of the firstequalizer 70 and the second equalizer 72 is added by an adder 44 andcomposed.

In FIG. 3, the aspect in which the reading element unit 38 includes thefirst reading element 40 and the second reading element 42 has beendescribed as an example. However, for example, even in a case where onlyone reading element (hereinafter, also referred to as a single readingelement) among a pair of reading elements is used, a signalcorresponding to a reproducing signal obtained from the reading elementunit 38 is obtained.

In this case, for example shown in FIG. 8, the reproducing signalobtained from the single reading element is allocated to a planeposition on a track calculated from a servo signal obtained by the servoelement pair 36 synchronously with the reproducing signal. By repeatingthis operation while moving the single reading element in the tape widthdirection, a two-dimensional image of the reproducing signal(hereinafter, simply referred to as a “two-dimensional image”) isobtained. Here, a reproducing signal configuring the two-dimensionalimage or a part of the two-dimensional image (for example, reproducingsignal corresponding to the position of the plurality of tracks) issignal corresponding to the reproducing signal obtained from the readingelement unit 38.

FIG. 18 shows an example of a two-dimensional image of the reproducingsignal of the magnetic tape MT in a loop shape (hereinafter, alsoreferred to as a “loop tape”) obtained by using a loop tester. Here, theloop tester indicates a device which transports the loop tape in a statewhere the loop tape is repeatedly in contact with the single readingelement, for example. In order to obtain a two-dimensional image in thesame manner as in the case of the loop tester, a reel tester may be usedor an actual tape drive may be used. The “reel tester” here indicates adevice which transports the magnetic tape MT in a reel state, forexample.

As described above, even in a case where a head for a magnetic tape ofthe related art which does not include the reading element unit on whichthe plurality of reading elements are loaded at adjacent positions isused, the effect according to the technology disclosed in thespecification can be quantitatively evaluated. As an example of an indexfor quantitatively evaluating the effect according to the technologydisclosed in the specification, an SNR, an error rate, and the like areused.

FIGS. 4 to 6 show results obtained from experiments performed by thepresent inventors. As an example shown in FIG. 4, a reading element pair50 are disposed on a track region 49. The track region 49 is a firsttrack 49A, a second track 49B, and a third track 49C adjacent to eachother in the tape width direction. The reading element pair 50 are afirst reading element 50A and a second reading element 50B. The firstreading element 50A and the second reading element 50B are disposed atpositions adjacent to each other in the tape width direction. The firstreading element 50A is disposed so as to face the second track 49B whichis the reading target track and fall in the second track 49B. Inaddition, the second reading element 50B is disposed so as to face thefirst track 49A adjacent to one side of the second track 49B and fall inthe first track 49A.

FIG. 5 shows an example of a correlation between an SNR regarding eachof a single reading element data item and a first composite data itemunder a first condition, and track off-set. In addition, FIG. 6 shows anexample of a correlation between an SNR regarding each of the singlereading element data item and a second composite data item under asecond condition, and track off-set.

Here, the single reading element data indicates data obtained byperforming a waveform equalization process with respect to data read bythe first reading element 50A, in the same manner as in the case of thefirst reading element 40 shown in FIG. 3. The first condition indicatesa condition in which a reading element pitch is 700 nm (nanometers). Thesecond condition indicates a condition in which a reading element pitchis 500 nm. The reading element pitch indicates a pitch of the firstreading element 50A and the second reading element 50B in the tape widthdirection, as shown in FIG. 4 as an example. The track off-set indicatesa deviation amount between the center of the second track 49B in thetape width direction and the center of the first reading element 50A inthe track width direction, as an example shown in FIG. 4.

The first composite data indicates data composed by adding a firstwaveform equalized data item and a second waveform equalized data itemobtained under the first condition. The first waveform equalized dataitem indicates data obtained by performing the waveform equalizationprocess with respect to the data read by the first reading element 50A,in the same manner as in the case of the first reading element 40 shownin FIG. 3. The second waveform equalized data item indicates dataobtained by performing the waveform equalization process with respect tothe data read by the second reading element 50B, in the same manner asin the case of the second reading element 42 shown in FIG. 3. The secondcomposite data indicates data composed by adding a first waveformequalized data item and a second waveform equalized data item obtainedunder the second condition.

In a case of comparing the SNR of the first composite data shown in FIG.5 to the SNR of the second composite data shown in FIG. 6, the SNR ofthe first composite data rapidly declines to generate a groove of thegraph, in a case where the track off-set is −0.4 μm (micrometers) to 0.2μm, whereas the SNR of the second composite data does not rapidlydecline as the graph of the SNR of the first composite data. Each of theSNR of the first composite data and the SNR of the second composite datais higher than the SNR of the single reading element data, andparticularly, the SNR of the second composite data is higher than theSNR of the single reading element data over the entire range of thetrack off-set.

From the experimental results shown in FIGS. 5 and 6, the presentinventors have found that it is preferable to perform the reading ofdata in a state where the first reading element 50A and the secondreading element 50B are adjacent to each other in the tape widthdirection, compared to a case where the reading of data is performed byonly the first reading element 50A. The “state adjacent to each other”here means that the first reading element 50A and the second readingelement 50B are not in contact with each other, but are disposed in aline in the tape width direction, so that the SNR becomes higher thanthe SNR of the single reading element data, over the entire range of thetrack off-set.

In one aspect, as an example shown in FIG. 3, in the reading elementunit 38, parts of the first reading element 40 and the second readingelement 42 are overlapped each other in the running direction, andaccordingly, a high density of the tracks included in the magnetic tapeMT is realized.

As shown in FIG. 7 as an example, the magnetic tape apparatus 10comprises an actuator 60, an extraction unit 62, an analog/digital (A/D)converters 64, 66, and 68, a decoding unit 69, and a computer 73.

The control device 18 is connected to the servo element pair 36 throughthe analog-to-digital (A/D) converter 68. The A/D converter 68 outputs aservo signal obtained by converting an analog signal obtained by readingthe servo pattern 32 by the servo elements 36A and 36B included in theservo element pairs 36 into a digital signal, to the control device 18.

The control device 18 is connected to the actuator 60. The actuator 60is attached to the reading head 16 and applies electric power to thereading head 16 under the control of the control device 18, to changethe position of the reading head 16 in the tape width direction. Theactuator 60, for example, includes a voice coil motor, and the electricpower applied to the reading head 16 is electric power obtained byconverting an electric energy based on a current flowing through thecoil into a kinetic energy, using an energy of a magnet as a medium.

Here, the aspect in which the voice coil motor is loaded on the actuator60 has been described. However, the magnetic tape apparatus is notlimited to the aspect, and for example, a piezoelectric element can alsobe used, instead of the voice coil motor. In addition, the voice coilmotor and the piezoelectric element can be combined with each other.

The deviation amount of the positions of the magnetic tape MT and thereading element unit 38 is determined in accordance with a servo signalwhich is a result obtained by reading the servo patterns 32 by the servoelement pair 36. The control device 18 controls the actuator 60 to applythe electric power according to the deviation amount of the positions ofthe magnetic tape MT and the reading element unit 38 to the reading head16. Accordingly, the position of the reading head 16 is changed in thetape width direction and the position of the reading head 16 is adjustedto a normal position. Here, for example shown in FIG. 3, the normalposition indicates a position of the reading head 16 in a default stateof the magnetic tape apparatus 10.

Here, the aspect in which the deviation amount of the positions of themagnetic tape MT and the reading element unit 38 is determined inaccordance with the servo signal which is the result obtained by readingof the servo pattern 32 by the servo element pair 36 is used as anexample. However, the magnetic tape apparatus is not limited to theaspect. For example, as the deviation amount of the positions of themagnetic tape MT and the reading element unit 38, the deviation amountof predetermined reference positions of the servo element 36A and themagnetic tape MT may be used, or the deviation amount of an end surfaceof the reading head 16 and a center position of a specific trackincluded in the magnetic tape MT may be used. As described above, thedeviation amount of the positions of the magnetic tape MT and thereading element unit 38 may be the deviation amount corresponding to thedeviation amount between the center of the reading target track 30A inthe tape width direction and the center of the reading head 16 in thetape width direction. Hereinafter, for convenience of description, thedeviation amount of the positions of the magnetic tape MT and thereading element unit 38 is simply referred to as a “deviation amount”.

For example shown in FIG. 8, the deviation amount is calculated based ona ratio of a distance A to a distance B. The distance A indicates adistance calculated from a result obtained by reading the first diagonalline 32A and the second diagonal line 32B adjacent to each other by theservo element 36A. The distance B indicates a distance calculated from aresult obtained by reading the two first diagonal lines 32A adjacent toeach other by the servo element 36A.

The extraction unit 62 comprises the control device 18 and atwo-dimensional FIR filter 71. The two-dimensional FIR filter 71comprises the adder 44, the first equalizer 70, and the second equalizer72.

The first equalizer 70 is connected to the first reading element 40through the A/D converter 64. In addition, the first equalizer 70 isconnected to each of the control device 18 and the adder 44. The dataread by the first reading element 40 from the specific track region 31is an analog signal, and the A/D converter 64 outputs a first readingsignal obtained by converting the data read by the first reading element40 from the specific track region 31 into a digital signal, to the firstequalizer 70.

The second equalizer 72 is connected to the second reading element 42through the A/D converter 66. In addition, the second equalizer 72 isconnected to each of the control device 18 and the adder 44. The dataread by the second reading element 42 from the specific track region 31is an analog signal, and the A/D converter 66 outputs a second readingsignal obtained by converting the data read by the second readingelement 42 from the specific track region 31 into a digital signal, tothe second equalizer 72. The first reading signal and the second readingsignal are one example of a “reading result for each reading element”.

The first equalizer 70 performs the waveform equalization process withrespect to the input first reading signal. For example, the firstequalizer 70 performs a convolution arithmetic operation of a tapcoefficient with respect to the input first reading signal, and outputsthe first arithmetic operation processed signal which is a signal afterthe arithmetic operation.

The second equalizer 72 performs the waveform equalization process withrespect to the input second reading signal. For example, the secondequalizer 72 performs a convolution arithmetic operation of a tapcoefficient with respect to the input second reading signal, and outputsthe second arithmetic operation processed signal which is a signal afterthe arithmetic operation.

Each of the first equalizer 70 and the second equalizer 72 outputs thefirst arithmetic operation processed signal and the second arithmeticoperation processed signal to the adder 44. The adder 44 adds andcomposes the first arithmetic operation processed signal input from thefirst equalizer 70 and the second arithmetic operation processed signalinput from the second equalizer 72, and outputs the composite dataobtained by the composite to the decoding unit 69.

Each of the first equalizer 70 and the second equalizer 72 is aone-dimensional FIR filter.

In one aspect, the FIR filter is a series of actual values includingpositive and negative values, the number of lines of the series isreferred to as a tap number, and the numerical value is referred to as atap coefficient. In addition, in one aspect, the waveform equalizationindicates a process of the convolution arithmetic operation of theseries of actual values, that is, the tap coefficient, with respect tothe reading signal. The “reading signal” here indicates a collectiveterm of the first reading signal and the second reading signal. In oneaspect, the equalizer indicates a circuit which carries out a process ofperforming the convolution arithmetic operation of the tap coefficientwith respect to the reading signal or the other input signal andoutputting the signal after the arithmetic operation. In addition, inone aspect, the adder indicates a circuit which simply adds two series.The weighting of the two series is reflected on the numerical values,that is, the tap coefficient of the FIR filter used in the firstequalizer 70 and the second equalizer 72.

The control device 18 performs the waveform equalization processaccording to the deviation amount with respect to each of the firstequalizer 70 and the second equalizer 72 by setting the tap coefficientaccording to the deviation amount with respect to the FIR filter of eachof the first equalizer 70 and the second equalizer 72.

The control device 18 comprises an association table 18A. Theassociation table 18A associates the tap coefficient with the deviationamount regarding each of the first equalizer 70 and the second equalizer72. A combination of the tap coefficient and the deviation amount is,for example, a combination obtained in advance as a combination of thetap coefficient and the deviation amount, with which the best compositedata is obtained by the adder 44, based on the result obtained byperforming at least one of the test performed with a real machine or asimulation. The “best composite data” here indicates data correspondingto the reading target track data.

Here, the “reading target track data” indicates “data derived from thereading target track 30A”. The “data derived from the reading targettrack 30A” indicates data corresponding to data written on the readingtarget track 30A. As an example of the data written on the readingtarget track 30A, data which is read from the reading target track 30Aand to which a noise component from the adjacent tracks is not mixed isused.

As described above, the association table 18A is used as an example. Inanother aspect, an arithmetic expression may be used instead of theassociation table 18A. The “arithmetic expression” here indicates anarithmetic expression in which an independent variable is set as thedeviation amount and a dependent variable is set as the tap coefficient,for example.

As described above, the aspect in which the tap coefficient is derivedfrom the association table 18A, in which combinations of the tapcoefficients and the deviation amounts are regulated, has beendescribed. In another aspect, for example, the tap coefficient may bederived from the association table in which the combinations of tapcoefficients and ratios are regulated, or the arithmetic expression. The“ratio” here indicates a ratio between an overlapping region with thereading target track 30A and an overlapping region with the adjacenttrack, regarding each of the first reading element 40 and the secondreading element 42. The ratio is calculated and specified from thedeviation amount by the control device 18 and the tap coefficient isdetermined in accordance with the specified ratio.

The decoding unit 69 decodes the composite data input from the adder 44and outputs a decoded signal obtained by the decoding to the computer73. The computer 73 performs various processes with respect to thedecoded signal input from the decoding unit 69.

Next, a magnetic tape reading process carried out by the extraction unit62 will be described with reference to FIG. 9. Hereinafter, forconvenience of description, the embodiment is described based onassumption that the servo signal is input to the control device 18, in acase where a period of the sampling comes. Here, the sampling is notlimited to the sampling of the servo signal and also means the samplingof the reading signal. That is, in one aspect, the track region 30 isformed in parallel with the servo pattern 32 along the runningdirection, and accordingly, the reading operation by the reading elementunit 38 is performed synchronously with the reading operation by theservo element pair 36.

In the process shown in FIG. 9, first, in a step S100, the controldevice 18 determines whether or not the period of the sampling comes. Inthe step S100, in a case where the period of the sampling comes, thedetermination is affirmative and the magnetic tape reading process movesto a step S102. In the step S100, in a case where the period of thesampling does not come, the determination is denied, and thedetermination of the step S100 is performed again.

In a step S102, the first equalizer 70 acquires a first reading signal,the second equalizer 72 acquires a second reading signal, and then, themagnetic tape reading process moves to a step S104.

In the step S104, the control device 18 acquires a servo signal andcalculates a deviation amount from the acquired servo signal, and thenthe magnetic tape reading process moves to a step S106.

In the step S106, the control device 18 derives a tap coefficientcorresponding to the deviation amount calculated in the process of thestep S104 from the association table 18A, regarding first to third tapsof each of the first equalizer 70 and the second equalizer 72. That is,by performing the process of the step S106, an optimal combination isdetermined as a combination of a one-dimensional FIR filter which is anexample of the first equalizer 70 and a one-dimensional filter which isan example of the second equalizer 72. The “optimal combination” hereindicates, for example, a combination in which the composite data outputby performing a process of a step S112 which will be described later isset as data corresponding to the reading target track data.

In the next step S108, the control device 18 sets the tap coefficientderived in the process of the step S106 with respect to each of thefirst equalizer 70 and the second equalizer 72, and then the magnetictape reading process moves to a step S110.

In the step S110, the first equalizer 70 performs the waveformequalization process with respect to the first reading signal acquiredin the process of the step S102, and accordingly, the first arithmeticoperation processed signal is generated. The first equalizer 70 outputsthe generated first arithmetic operation processed signal to the adder44. The second equalizer 72 performs the waveform equalization processwith respect to the second reading signal acquired in the process of thestep S102, and accordingly, the second arithmetic operation processedsignal is generated. The second equalizer 72 outputs the generatedsecond arithmetic operation processed signal to the adder 44.

In the next step S112, the adder 44 adds and composes the firstarithmetic operation processed signal input from the first equalizer 70and the second arithmetic operation processed signal input from thesecond equalizer 72, as shown in FIG. 10 as an example. The adder 44outputs the composite data obtained by the composite to the decodingunit 69.

In a case where the reading element unit 38 is disposed in the specifictrack region 31, as the example shown in FIG. 3, the data correspondingto the reading target track data, from which the noise component fromthe first noise mixing source track 30B is removed, is output as thecomposite data, by performing the process of the step S112. That is, byperforming the process of the step S102 to the step S112, the extractionunit 62 extracts only the data derived from the reading target track30A.

In a case where the magnetic tape MT expands and contracts in the tapewidth direction or vibration is applied to at least one of the magnetictape MT or the reading head 16, the reading element unit 38 is displacedto a position shown in FIG. 11 from the position shown in FIG. 3 as anexample. In the example shown in FIG. 11, the first reading element 40and the second reading element 42 are disposed at positions straddlingover both of the reading target track 30A and the second noise mixingsource track 30C. In this case, by performing the process of the stepS102 to the step S112, the data corresponding to the reading targettrack data, from which the noise component from the second noise mixingsource track 30C is removed, is output to the decoding unit 69 as thecomposite data.

In the next step S114, the control device 18 determines whether or not acondition for completing the magnetic tape reading process (hereinafter,referred to as a “completion condition”) is satisfied. The completioncondition indicates, for example a condition in which the entiremagnetic tape MT is wound around the winding reel 22, a condition inwhich an instruction for forced completion of the magnetic tape readingprocess is applied from the outside, and the like.

In the step S114, in a case where the completion condition is notsatisfied, the determination is denied, and the magnetic tape readingprocess is moved to the step S100. In the step S114, in a case where thecompletion condition is satisfied, the determination is affirmative, andthe magnetic tape reading process ends.

As described above, in one aspect of the magnetic tape apparatus 10, thedata from the specific track region 31 is read by each of the firstreading element 40 and the second reading element 42 disposed in a stateof being adjacent to each other. In addition, the extraction unit 62performs the waveform equalization process according to the deviationamount with respect to each of the first reading element 40 and thesecond reading element 42, to extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal. Therefore, in the magnetic tape apparatus 10, it is possible toprevent a deterioration in reproducing quality of data read from thereading target track 30A by the linear scanning method, compared to acase where the data is read from the reading target track 30A only by asingle reading element by the linear scanning method.

In one aspect of the magnetic tape apparatus 10, parts of the firstreading element 40 and the second reading element 42 are overlapped eachother in the running direction. Therefore, in the magnetic tapeapparatus 10, it is possible to increase reproducing quality of dataread from the reading target track 30A by the linear scanning method,compared to a case where the entire portions of the plurality of readingelements are overlapped in the running direction.

In one aspect of the magnetic tape apparatus 10, the specific trackregion 31 is the reading target track 30A, the first noise mixing sourcetrack 30B, and the second noise mixing source track 30C, and each of thefirst reading element 40 and the second reading element 42 straddlesover both of the reading target track 30A and the adjacent track, in acase where a positional relationship with the magnetic tape MT ischanged. Therefore, in the magnetic tape apparatus 10, it is possible toreduce the noise component generated in one of the reading element ofthe first reading element 40 and the second reading element 42 due toentering the adjacent track from the reading target track 30A in thetape width direction, by using the reading result obtained by the otherreading element entering the adjacent track from the reading targettrack 30A in the tape width direction, compared to a case where the datais read by only the single reading element from the reading target track30A by the linear scanning method.

In one aspect of the magnetic tape apparatus 10, the tap coefficientused in the waveform equalization process is determined in accordancewith the deviation amount. Therefore, in the magnetic tape apparatus 10,it is possible to instantaneously reduce the noise component generateddue to the entering the reading target track 30A from the adjacent trackin the tape width direction, in accordance with a change of thepositional relationship between the magnetic tape MT and the readingelement unit 38, compared to a case where the tap coefficient isdetermined in accordance with a parameter with no relation with thedeviation amount.

In one aspect of the magnetic tape apparatus 10, regarding each of thefirst reading element 40 and the second reading element 42, the ratiobetween the overlapping region with the reading target track 30A and theoverlapping region with the adjacent track is specified from thedeviation amount, and the tap coefficient according to the specifiedratio is determined. Therefore, in the magnetic tape apparatus 10, it ispossible to exactly reduce the noise component, even in a case where thepositional relationship between the magnetic tape MT and the readingelement unit 38 is changed, compared to a case where the tap coefficientis determined in accordance with a parameter with no relation with aratio between the overlapping region with the reading target track 30Aand the overlapping region with the adjacent track regarding each of theplurality of reading elements.

In one aspect of the magnetic tape apparatus 10, the deviation amount isdetermined in accordance with the result obtained by reading the servopatterns 32 by the servo element pair 36. Therefore, in the magnetictape apparatus 10, it is possible to easily determine the deviationamount, compared to a case where the servo patterns 32 are not appliedto the magnetic tape MT.

In one aspect of the magnetic tape apparatus 10, the reading operationby the reading element unit 38 is performed synchronously with thereading operation by the servo element pair 36. Therefore, in themagnetic tape apparatus 10, it is possible to instantaneously reduce thenoise component generated due to the entering the reading target trackfrom the adjacent track in the width direction of the magnetic tape,compared to a case of a magnetic disk and a magnetic tape in a helicalscanning method, in which a servo pattern and data cannot besynchronously read.

In one aspect of the magnetic tape apparatus 10, the extraction unit 62includes the two-dimensional FIR filter 71. Each result obtained byperforming the waveform equalization process with respect to each of thefirst reading signal and the second reading signal is composed by thetwo-dimensional FIR filter 71, and accordingly, the data derived fromthe reading target track 30A is extracted from the first reading signaland the second reading signal. Therefore, in the magnetic tape apparatus10, it is possible to rapidly extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal, compared to a case of using only a one-dimensional FIR filter.In addition, in the magnetic tape apparatus 10, it is possible torealize simple calculation due to a smaller operation amount, comparedto a case of performing a matrix operation.

In one aspect of the magnetic tape apparatus 10, the first readingelement 40 and the second reading element 42 are used as a pair ofreading elements. Therefore, in the magnetic tape apparatus 10, it ispossible to contribute to miniaturization of the reading element unit38, compared to a case of using three or more reading elements. Byminiaturizing the reading element unit 38, the reading unit 26 and thereading head 16 can also be miniaturized. In addition, in the magnetictape apparatus 10, it is possible to prevent occurrence of a situationin which the reading element units 38 adjacent to each other are incontact with each other.

In one aspect of the magnetic tape apparatus 10, each of the pluralityof reading element units 38 reads data from the corresponding readingtarget track 30A included in each of the plurality of specific trackregions 31 by the linear scanning method. Therefore, in the magnetictape apparatus 10, it is possible to rapidly complete the reading ofdata from the plurality of reading target tracks 30A, compared to a casewhere the data is read by only the single reading element unit 38 fromeach of the plurality of reading target tracks 30A.

In the aspect, in a default state of the magnetic tape apparatus 10,each of the first reading element 40 and the second reading element 42is provided to straddle over both of the reading target track 30A andthe first noise mixing source track 30B, but the magnetic tape apparatusis not limited to the aspect. In an example shown in FIG. 12, a readingelement unit 138 is used instead of the reading element unit 38described above. The reading element unit 138 comprises a first readingelement 140 and a second reading element 142. In a default state of themagnetic tape apparatus 10, the center of the first reading element 140in the tape width direction coincides with a center CL of the readingtarget track 30A in the tape width direction. In a default state of themagnetic tape apparatus 10, the first reading element 140 and the secondreading element 142 fall in the reading target track 30A, without beingprotruded to the first noise mixing source track 30B and the secondnoise mixing source track 30C. In addition, in a default state of themagnetic tape apparatus 10, parts of the first reading element 140 andthe second reading element 142 are provided to be overlapped each otherin the running direction, in the same manner as the case of the firstreading element 40 and the second reading element 42 described in theembodiment.

As shown in FIG. 12 as an example, even in a state where the firstreading element 140 and the second reading element 142 face the readingtarget track 30A, without being protruded from the reading target track30A, a positional relationship between the reading element unit 138 andthe magnetic tape MT may be changed. That is, the reading element unit138 may straddle over the reading target track 30A and the first noisemixing source track 30B, or the reading element unit 138 may straddleover the reading target track 30A and the second noise mixing sourcetrack 30C. Even in these cases, by performing the processes in the stepS102 to the step S112 described above, it is possible to obtain the datacorresponding to the reading target track data, from which the noisecomponent from the first noise mixing source track 30B or the secondnoise mixing source track 30C is removed.

In addition, parts of the first reading element 140 and the secondreading element 142 are disposed at position to be overlapped each otherin the running direction, and accordingly, the second reading element142 can read the data from a portion of the reading target track 30Awhere the reading cannot be performed by the first reading element 140.As a result, it is possible to increase reliability of the readingtarget track data, compared to a case where the first reading element140 singly reads the data from the reading target track 30A.

As shown in FIG. 11 as an example, in a default state of the magnetictape apparatus 10, each of the first reading element 40 and the secondreading element 42 may be disposed at a position to straddle over bothof the reading target track 30A and the second noise mixing source track30C.

As described above, the reading element unit 38 including the firstreading element 40 and the second reading element 42 has been described.However, the magnetic tape apparatus is not limited to the aspect. In anexample shown in FIG. 13, a reading element unit 238 may be used insteadof the reading element unit 38. The reading element unit 238 isdifferent from the reading element unit 38, in a point that a thirdreading element 244 is included. In a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at a positionwhere a part thereof is overlapped with a part of the first readingelement 40 in the running direction. In addition, in a default state ofthe magnetic tape apparatus 10, the third reading element 244 isdisposed at a position to straddle over the reading target track 30A andthe second noise mixing source track 30C.

In this case, a third equalizer (not shown) is also allocated to thethird reading element 244, in the same manner as a case where the firstequalizer 70 is allocated to the first reading element 40 and the secondequalizer 72 is allocated to the second reading element 42. The thirdequalizer also has the same function as that of the first equalizer andthe second equalizer described above, and performs a waveformequalization process with respect to a third reading signal obtained byreading performed by the third reading element 244. The third equalizerperforms a convolution arithmetic operation of a tap coefficient withrespect to the third reading signal and outputs the third arithmeticoperation processed signal which is a signal after the arithmeticoperation. The adder 44 adds and composes a first arithmetic operationprocessed signal corresponding to the first reading signal, a secondarithmetic operation processed signal corresponding to the secondreading signal, the third arithmetic operation processed signalcorresponding to the third reading signal, and outputs the compositedata obtained by the composite to the decoding unit 69.

In the example shown in FIG. 13, in a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at the positionstraddling over the reading target track 30A and the second noise mixingsource track 30C, but the technology of the present disclosure is notlimited thereto. In a default state of the magnetic tape apparatus 10,the third reading element 244 may be disposed at the position facing thereading target track 30A, without being protruded from the readingtarget track 30A.

As described above, the reading element unit 38 has been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, the reading element pair 50 shown in FIG. 4 may be used insteadof the reading element unit 38. In this case, the first reading element50A and the second reading element 50B are set to be disposed atpositions adjacent to each other in the tape width direction. Inaddition, the first reading element 50A and the second reading element50B are set to be disposed in a line in the tape width direction so thatthe SNR is higher than the SNR of the single reading element data overthe entire range of the track off-set, as shown in FIG. 6 as an example,without being in contact with each other.

In the example shown in FIG. 4, for example, the first reading element50A falls in the second track 49B in a plan view, and the second readingelement 50B falls in the first track 49A in a plan view.

As described above, the servo element pair 36 have been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, one of the servo elements 36A and 36B may be used instead ofthe servo element pair 36.

As described above, the aspect in which the plurality of specific trackregions 31 are arranged in the track region 30 at regular interval inthe tape width direction has been described. However, the magnetic tapeapparatus is not limited to the aspect. For example, in two specifictrack regions 31 adjacent to each other in the plurality of specifictrack regions 31, one specific track region 31 and the other specifictrack region 31 may be arranged in the tape width direction so as to beoverlapped by the area of one track in the tape width direction. In thiscase, one adjacent track included in one specific track region 31 (forexample, first noise mixing source track 30B) becomes the reading targettrack 30A in the other specific track region 31. In addition, thereading target track 30A included in one specific track region 31becomes the adjacent track region (for example, second noise mixingsource track 30C) in the other specific track region 31.

The configuration of the magnetic tape apparatus and the magnetic tapereading process described above are merely an example. Accordingly,unnecessary steps can be removed, new steps can be added, and theprocess procedure can be changed, within a range not departing from thegist.

The magnetic tape apparatus can perform the reading (reproducing) ofdata recorded on the magnetic tape, and can also have a configurationfor recording data on the magnetic tape.

Magnetic Tape

Next, the magnetic tape on which the reading of the data is performed inthe magnetic tape apparatus will be described in detail.

In the invention and the specification, the “vacuum heating” of themagnetic tape is performed by holding the magnetic tape in anenvironment of a pressure of 200 Pa to 0.01 MPa and at an atmospheretemperature of 70° C. to 90° C. for 24 hours.

In the invention and the specification, the spacing measured by opticalinterferometry regarding the surface of the magnetic layer of themagnetic tape is a value measured by the following method. In theinvention and the specification, the “surface of the magnetic layer” ofthe magnetic tape is identical to the surface of the magnetic tape onthe magnetic layer side.

In a state where the magnetic tape and a transparent plate-shaped member(for example, glass plate or the like) are overlapped onto each other sothat the surface of the magnetic layer of the magnetic tape faces thetransparent plate-shaped member, a pressing member is pressed againstthe side of the magnetic tape opposite to the magnetic layer side atpressure of 5.05×10⁴ N/m (0.5 atm). In this state, the surface of themagnetic layer of the magnetic tape is irradiated with light through thetransparent plate-shaped member (irradiation region: 150,000 to 200,000μm²), and a spacing (distance) between the surface of the magnetic layerof the magnetic tape and the surface of the transparent plate-shapedmember on the magnetic tape side is acquired based on intensity (forexample, contrast of interference fringe image) of interference lightgenerated due to a difference in a light path between reflected lightfrom the surface of the magnetic layer of the magnetic tape andreflected light from the surface of the transparent plate-shaped memberon the magnetic tape side. The light emitted here is not particularlylimited. In a case where the emitted light is light having an emissionwavelength over a comparatively wide wavelength range as white lightincluding light having a plurality of wavelengths, a member having afunction of selectively cutting light having a specific wavelength or awavelength other than wavelengths in a specific wavelength range, suchas an interference filter, is disposed between the transparentplate-shaped member and a light receiving unit which receives reflectedlight, and light at some wavelengths or in some wavelength ranges of thereflected light is selectively incident to the light receiving unit. Ina case where the light emitted is light (so-called monochromatic light)having a single luminescence peak, the member described above may not beused. The wavelength of light incident to the light receiving unit canbe set to be 500 to 700 nm, for example. However, the wavelength oflight incident to the light receiving unit is not limited to be in therange described above. In addition, the transparent plate-shaped membermay be a member having transparency through which emitted light passes,to the extent that the magnetic tape is irradiated with light throughthis member and interference light is obtained.

The measurement described above can be performed by using a commerciallyavailable tape spacing analyzer (TSA) such as Tape Spacing Analyzermanufactured by Micro Physics, Inc., for example. The spacingmeasurement of the examples was performed by using Tape Spacing Analyzermanufactured by Micro Physics, Inc.

In addition, the full width at half maximum of spacing distribution ofthe invention and the specification is a full width at half maximum(FWHM), in a case where the interference fringe image obtained by themeasurement of the spacing described above is divided into 300,000points, a spacing of each point (distance between the surface of themagnetic layer of the magnetic tape and the surface of the transparentplate-shaped member on the magnetic tape side) is acquired, this spacingis shown with a histogram, and this histogram is fit with Gaussiandistribution.

Further, the difference (S_(after)−S_(before)) is a value obtained bysubtracting a mode before the vacuum heating from a mode after thevacuum heating of the 300,000 points.

A portion (projection) which mainly comes into contact (so-called realcontact) with the reading element in a case where the magnetic tape andthe reading element slide on each other during the reproducing, and aportion (hereinafter, referred to as a “base portion”) having a heightlower than that of the portion described above are normally present onthe surface of the magnetic layer. The inventors have surmised that thespacing described above is a value which is an index of a distancebetween the reading element and the base portion in a case where themagnetic tape and the reading element slide on each other. However, itis thought that, in a case where a lubricant included on the magneticlayer forms a liquid film on the surface of the magnetic layer, theliquid film is present between the base portion and the reading element,and thus, the spacing is narrowed by the thickness of the liquid film.

Meanwhile, the lubricant is generally divided broadly into a fluidlubricant and a boundary lubricant. Fatty acid ester included in themagnetic layer of the magnetic tape is known as a component which canfunction as a fluid lubricant. It is considered that a fluid lubricantcan protect the surface of the magnetic layer by forming a liquid filmon the surface of the magnetic layer. The inventors have thought thatthe presence of the liquid film of fatty acid ester on the surface ofthe magnetic layer contributes to the smooth sliding (improvement ofsliding properties) between the magnetic tape and the reading element.However, an excessive amount of fatty acid ester present on the surfaceof the magnetic layer causes sticking due to the formation of a meniscus(liquid crosslinking) between the surface of the magnetic layer and thereading element due to fatty acid ester, thereby decreasing slidingproperties.

In regards to this point, it is surmised that, fatty acid ester is acomponent having properties of volatilizing by vacuum heating, and thedifference (S_(after)−S_(before)) of a spacing between a state after thevacuum heating (state in which a liquid film of fatty acid ester isvolatilized and removed) and a state before the vacuum heating (state inwhich the liquid film of fatty acid ester is present) may be an index ofa thickness of the liquid film formed of fatty acid ester on the surfaceof the magnetic layer. The inventors have surmised that the presence ofthe liquid film of fatty acid ester on the surface of the magneticlayer, so that the value is greater than 0 nm and equal to or smallerthan 12.0 nm, causes the improvement of sliding properties between thereading element and the magnetic tape while preventing sticking.

A smaller value of the full width at half maximum of spacingdistribution means that a variation in the values of the spacingmeasured on each part of the surface of the magnetic layer is small. Itis thought that it is effective to increase uniformity of a contactstate between the surface of the magnetic layer and the reading element,by increasing uniformity of a height of projection present on thesurface of the magnetic layer and increasing uniformity of a thicknessof a liquid film of fatty acid ester, in order to realize smooth slidingbetween the magnetic tape and the reading element.

In regards to this point, it is considered that the reason for thevariation in values of the spacing is a variation in height of theprojection of the surface of the magnetic layer and a variation in thethickness of the liquid film fatty acid ester. The inventors havethought that the full width at half maximum of the spacing distributionFWHM_(before) measured before the vacuum heating, that is, in a statewhere the liquid film of fatty acid ester is present on the surface ofthe magnetic layer, becomes great, as the variation in height of theprojection and the variation in the thickness of the liquid film offatty acid ester are great. Particularly, the spacing distributionFWHM_(before) is greatly affected by the variation in the thickness ofthe liquid film of fatty acid ester. In contrast, the inventors havesurmised that the full width at half maximum of the spacing distributionFWHM_(after) measured after the vacuum heating, that is, in a statewhere the liquid film of fatty acid ester is removed from the surface ofthe magnetic layer, becomes great, as the variation in height of theprojection is great. That is, the inventors have surmised that smallfull widths at half maximum of spacing distributions FWHM_(before) andFWHM_(after) mean a small variation in the thickness of the liquid filmof fatty acid ester on the surface of the magnetic layer and a smallvariation in height of the projection. It is thought that an increase inuniformity of the height of the projection and the thickness of theliquid film of fatty acid ester so that the full widths at half maximumof the spacing distribution FWHM_(before) and FWHM_(after) are greaterthan 0 nm and equal to or smaller than 15.0 nm contribute to smoothsliding between the magnetic tape and the reading element.

By doing so, it is thought that it is possible to prevent the positionalchange on a small cycle described above, by improving sliding propertiesbetween the magnetic tape and the reading element. It is surmised thatthis contributes to setting more suitable waveform equalization processto be performed with respect to the reading result obtained by thereading at each portion.

However, the above surmises do not limit the invention.

Full Width at Half Maximum of Spacing Distribution FWHM_(before) andFWHM_(after)

Both of the full width at half maximum of spacing distributionFWHM_(before) before the vacuum heating and the full width at halfmaximum of spacing distribution FWHM_(after) after the vacuum heatingwhich are measured in the magnetic tape are greater than 0 nm and equalto or smaller than 15.0 nm. As described above, it is surmised that thiscontributes to setting more suitable waveform equalization process to beperformed with respect to the reading result obtained by reading at eachportion. From the viewpoint described above, the FWHM_(before) and theFWHM_(after) are preferably equal to or smaller than 14.0 nm, morepreferably equal to or smaller than 13.0 nm, even more preferably equalto or smaller than 12.0 nm, still preferably equal to or smaller than11.0 nm, and still more preferably equal to or smaller than 10.0 nm. TheFWHM_(before) and the FWHM_(after) can be, for example, equal to orgreater than 0.5 nm, equal to or greater than 1.0 nm, equal to orgreater than 2.0 nm, or equal to or greater than 3.0 nm. Meanwhile, asmall value is preferable from the viewpoint described above, andtherefore, the values thereof may be smaller than the exemplifiedvalues.

The full width at half maximum of spacing distribution FWHM_(before)before the vacuum heating can be decreased mainly by decreasing thevariation in the thickness of the liquid film of fatty acid ester. Anexample of a specific method will be described later. Meanwhile, thefull width at half maximum of spacing distribution FWHM_(after) afterthe vacuum heating can be decreased by decreasing the variation inheight of the projection of the surface of the magnetic layer. In orderto realize the decrease described above, it is preferable that apresence state of the powder component included in the magnetic layer,for example, non-magnetic filler, which will be described laterspecifically, in the magnetic layer is controlled. An example of aspecific method will be described later.

Difference (S_(after)−S_(before))

The difference (S_(after)−S_(before)) of the spacings before and afterthe vacuum heating measured in the magnetic tape is greater than 0 nmand equal to or smaller than 12.0 nm. As described above, it is surmisedthat this point also contributes to setting more suitable waveformequalization process to be performed with respect to the reading resultobtained by reading at each portion. From the viewpoint described above,the difference (S_(after)−S_(before)) is preferably equal to or greaterthan 0.1 nm, more preferably equal to or greater than 1.0 nm, even morepreferably equal to or greater than 1.5 nm, still more preferably equalto or greater than 2.0 nm, and still even more preferably equal to orgreater than 2.5 nm. In addition, from the same viewpoint, thedifference (S_(after)−S_(before)) is preferably equal to or smaller than11.0 nm, more preferably equal to or smaller than 10.0 nm, even morepreferably equal to or smaller than 9.0 nm, still preferably equal to orsmaller than 8.0 nm, still more preferably equal to or smaller than 7.0nm, still even more preferably equal to or smaller than 6.0 nm, stillfurthermore preferably equal to or smaller than 5.0 nm, and still evenfurthermore preferably equal to or smaller than 4.0 nm. The difference(S_(after)−S_(before)) can be controlled by the amount of fatty acidester added to a magnetic layer forming composition. In addition,regarding the magnetic tape including a non-magnetic layer between thenon-magnetic support and the magnetic layer, the difference(S_(after)−S_(before)) can also be controlled by the amount of fattyacid ester added to a non-magnetic layer forming composition. This isbecause that the non-magnetic layer can play a role of holding alubricant and supplying the lubricant to the magnetic layer, and fattyacid ester included in the non-magnetic layer may be moved to themagnetic layer and present in the surface of the magnetic layer.

Next, the magnetic layer and the like included in the magnetic tape willbe described more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder included in the magnetic layer,ferromagnetic powder normally used in the magnetic layer of variousmagnetic recording media can be used. It is preferable to useferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density of the magnetic tape. Fromthis viewpoint, an average particle size of the ferromagnetic powder ispreferably equal to or smaller than 50 nm, more preferably equal to orsmaller than 45 nm, even more preferably equal to or smaller than 40 nm,still preferably equal to or smaller than 35 nm, still preferably equalto or smaller than 30 nm, still more preferably equal to or smaller than25 nm, and still even more preferably equal to or smaller than 20 nm.Meanwhile, the average particle size of the ferromagnetic powder ispreferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm, from a viewpoint of stabilityof magnetization.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is to be understood to mean ferromagnetic powder from which a hexagonalferrite type crystal structure can be detected as a main phase by X-raydiffraction analysis. The main phase is to be understood to mean astructure to which the diffraction peak with the highest intensity in anX-ray diffraction spectrum obtained by X-ray diffraction analysis isassigned. For example, when the diffraction peak with the highestintensity in an X-ray diffraction spectrum obtained by X-ray diffractionanalysis is assigned to the hexagonal ferrite type crystal structure, itshall be determined that the hexagonal ferrite type crystal structure isdetected as a main phase. When a single structure is only detected byX-ray diffraction analysis, this detected structure is determined as amain phase. The hexagonal ferrite type crystal structure at leastcontains, as constitutional atoms, an iron atom, a divalent metal atom,and an oxygen atom. A divalent metal atom is a metal atom which canconvert into a divalent cation as an ion thereof, and examples thereofinclude alkaline earth metal atoms, such as a strontium atom, a bariumatom, and a calcium atom, and a lead atom. In the invention and thespecification, the hexagonal strontium ferrite powder is to beunderstood to mean powder in which a main divalent metal atom containedtherein is a strontium atom, and the hexagonal barium ferrite powder isto be understood to mean powder in which a main divalent metal atomcontained therein is a barium atom. The main divalent metal atom is tobe understood to mean a divalent metal atom having the highest contentin terms of atom % among divalent metal atoms contained in this powder.However, the divalent metal atom does not include rare earth atoms. Inthe invention and the specification, the rare earth atoms are selectedfrom the group consisting of a scandium atom (Sc), an yttrium atom (Y),and a lanthanoid atom. The lanthanoid atom is selected from the groupconsisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymiumatom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samariumatom (Sm), an europium atom (Eu), a gadolinium atom (Gd), a terbium atom(Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er),a thulium atom (Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspectof the hexagonal ferrite powder will be described in more detail.

The activation volume of the hexagonal strontium ferrite powder ispreferably 800 to 1,600 nm³. The atomized hexagonal strontium ferritepowder showing the activation volume in the range described above issuitable for manufacturing a magnetic tape exhibiting excellentelectromagnetic conversion characteristics. The activation volume of thehexagonal strontium ferrite powder is preferably equal to or greaterthan 800 nm³ and can also be, for example equal to or greater than 850nm³. In addition, from a viewpoint of further improving electromagneticconversion characteristics, the activation volume of the hexagonalstrontium ferrite powder is more preferably equal to or smaller than1,500 nm³, even more preferably equal to or smaller than 1,400 nm³,still preferably equal to or smaller than 1,300 nm³, still morepreferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same can be appliedto the activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using a vibrating sample magnetometer(measurement temperature: 23° C.±1° C.), and the activation volume andthe anisotropy constant Ku are values acquired from the followingrelational expression of He and an activation volume V. A unit of theanisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include rare earthatom. In a case where the hexagonal strontium ferrite powder includesrare earth atom, it preferably includes rare earth atom in a content(bulk content) of 0.5 to 5.0 atom %, with respect to 100 atom % of ironatom is 0.5 to 5.0 atom %. In one aspect, the hexagonal strontiumferrite powder which includes rare earth atom can have a rare earth atomsurface portion uneven distribution. The “rare earth atom surfaceportion uneven distribution” of the invention and the specificationmeans that a rare earth atom content with respect to 100 atom % of ironatom in a solution obtained by partially dissolving the hexagonalstrontium ferrite powder with acid (referred to as a “rare earth atomsurface portion content” or simply as a “surface portion content” forrare earth atom) and a rare earth atom content with respect to 100 atom% of iron atom in a solution obtained by totally dissolving thehexagonal strontium ferrite powder with acid (referred to as a “rareearth atom bulk content” or simply as a “bulk content” for rare earthatom) satisfy a ratio of “rare earth atom surface portion content/rareearth atom bulk content >1.0”. The rare earth atom content of thehexagonal strontium ferrite powder is identical to the bulk content.With respect to this, the partial dissolving using acid is to dissolvethe surface portion of particles configuring the hexagonal strontiumferrite powder, and accordingly, the rare earth atom content in thesolution obtained by the partial dissolving is the rare earth atomcontent in the surface portion of the particles configuring thehexagonal strontium ferrite powder. The rare earth atom surface portioncontent satisfying a ratio of “rare earth atom surface portioncontent/rare earth atom bulk content >1.0” means that the rare earthatoms are unevenly distributed in the surface portion (that is, a largeramount of the rare earth atom is present, compared to that inside), inthe particles configuring the hexagonal strontium ferrite powder. Thesurface portion of the specification and the specification means a partof the region of the particles configuring the hexagonal strontiumferrite powder from the inside from the surface.

In a case where the hexagonal strontium ferrite powder includes rareearth atom, the hexagonal strontium ferrite powder preferably includesrare earth atom having a content (bulk content) of 0.5 to 5.0 atom %with respect to 100 atom % of an iron atom. It is surmised that the rareearth atom having the bulk content in the range described above anduneven distribution of the rare earth atom in the surface portion of theparticles configuring the hexagonal strontium ferrite powder contributeto prevention of a decrease in reproducing output during repeatedreproducing. This is surmised that it is because the anisotropy constantKu can be increased due to the rare earth atom having the bulk contentin the range described above included in the hexagonal strontium ferritepowder and the uneven distribution of the rare earth atom in the surfaceportion of the particles configuring the hexagonal strontium ferritepowder. As the value of the anisotropy constant Ku is high, occurrenceof a phenomenon which is so-called thermal fluctuation can be prevented(that is, thermal stability can be improved). By preventing occurrenceof thermal fluctuation, a decrease in reproducing output during repeatedreproducing can be prevented. This is surmised that, the unevendistribution of the rare earth atom in the surface portion of theparticles of the hexagonal strontium ferrite powder may contribute tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface portion, thereby increasing the anisotropy constant Ku.

In addition, it is also surmised that, by using the hexagonal strontiumferrite powder having a rare earth atom surface portion unevendistribution as ferromagnetic powder of the magnetic layer, chipping ofthe surface of the magnetic layer due to sliding with a magnetic headcan be prevented. That is, it is surmised that the hexagonal strontiumferrite powder having a rare earth atom surface portion unevendistribution also contributes to improvement of running durability of amagnetic tape. It is surmised that, this is because the unevendistribution of the rare earth atom in the surface of the particlesconfiguring the hexagonal strontium ferrite powder contributes to aninteraction between the surface of the particles and an organicsubstance (for example, binding agent and/or additive) included in themagnetic layer, thereby improving hardness of the magnetic layer.

From a viewpoint of further preventing a decrease in reproducing outputduring repeated running and/or a viewpoint of further improving runningdurability, the rare earth atom content (bulk content) is preferably 0.5to 4.5 atom %, more preferably 1.0 to 4.5 atom %, and even morepreferably 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder which includesrare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atom are included, the bulkcontent is obtained from the total of the two or more kinds of rareearth atom. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of further preventing a decrease in reproducing outputduring repeated reproducing include a neodymium atom, a samarium atom,an yttrium atom, and a dysprosium atom, a neodymium atom, a samariumatom, an yttrium atom are more preferable, and a neodymium atom is evenmore preferable.

In the hexagonal strontium ferrite powder having a rare earth atomsurface portion uneven distribution, a degree of uneven distribution ofthe rare earth atom is not limited, as long as the rare earth atom isunevenly distributed in the surface portion of the particles configuringthe hexagonal strontium ferrite powder. For example, regarding thehexagonal strontium ferrite powder, a ratio of the surface portioncontent of the rare earth atom obtained by partial dissolving performedunder the dissolving conditions exemplified below and the bulk contentof the rare earth atom obtained by total dissolving performed under thedissolving conditions exemplified below, “surface portion content/bulkcontent” is greater than 1.0 and can be equal to or greater than 1.5.The surface portion content satisfying a ratio of “surface portioncontent/bulk content >1.0” means that the rare earth atoms are unevenlydistributed in the surface portion (that is, a larger amount of the rareearth atoms is present, compared to that inside), in the particlesconfiguring the hexagonal strontium ferrite powder. In addition, theratio of the surface portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions exemplifiedbelow and the bulk content of the rare earth atom obtained by totaldissolving performed under the dissolving conditions exemplified below,“surface portion content/bulk content” can be, for example, equal to orsmaller than 10.0, equal to or smaller than 9.0, equal to or smallerthan 8.0, equal to or smaller than 7.0, equal to or smaller than 6.0,equal to or smaller than 5.0, or equal to or smaller than 4.0. However,the “surface portion content/bulk content” is not limited to theexemplified upper limit or the lower limit, as long as the rare earthatom is unevenly distributed in the surface portion of the particlesconfiguring the hexagonal strontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by amethod disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed at the time of the completion of the dissolving. For example,by performing the partial dissolving, a region of the particlesconfiguring the hexagonal strontium ferrite powder which is 10% to 20%by mass with respect to 100% by mass of a total of the particles can bedissolved. On the other hand, the total dissolving means dissolvingperformed until the hexagonal strontium ferrite powder remaining in thesolution is not visually confirmed at the time of the completion of thedissolving.

The partial dissolving and the measurement of the surface portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10ml of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the solution obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface portion content. The same applies to the measurement of the bulkcontent.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10ml of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface portion content, and the bulk contentwith respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing information recorded on a magnetic tape, it is desirablethat the mass magnetization σs of ferromagnetic powder included in themagnetic tape is high. In regards to this point, in hexagonal strontiumferrite powder which includes the rare earth atom but does not have therare earth atom surface portion uneven distribution, σs tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it issurmised that, hexagonal strontium ferrite powder having the rare earthatom surface portion uneven distribution is preferable for preventingsuch a significant decrease in σs. In one aspect, σs of the hexagonalstrontium ferrite powder can be equal to or greater than 45 A·m²/kg andcan also be equal to or greater than 47 A·m²/kg. On the other hand, froma viewpoint of noise reduction, σs is preferably equal to or smallerthan 80 A·m²/kg and more preferably equal to or smaller than 60 A·m²/kg.σs can be measured by using a known measurement device capable ofmeasuring magnetic properties such as a vibrating sample magnetometer.Unless stated otherwise, the mass magnetization σs is a value measuredat a magnetic field strength of 15 kOe. With regard to the unit of as, 1[kOe]=10⁶/4π[A/m]

With regard to the contents (bulk contents) of the constituting atoms ofthe hexagonal strontium ferrite powder, the content of the strontiumatom in the hexagonal strontium ferrite powder can be, for example, 2.0to 15.0 atom % with respect to 100 atom % of the iron atom. In oneaspect, in the hexagonal strontium ferrite powder, the divalent metalatom included in this powder can be only a strontium atom. In anotheraspect, the hexagonal strontium ferrite powder can also include one ormore kinds of other divalent metal atoms, in addition to the strontiumatom. For example, a barium atom and/or a calcium atom can be included.In a case where the divalent metal atom other than the strontium atom isincluded, a content of a barium atom and a content of a calcium atom inthe hexagonal strontium ferrite powder respectively can be, for example,0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one aspect, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, an oxygen atom, may include a rare earthatom, and may or may not include atoms other than these atoms. As anexample, the hexagonal strontium ferrite powder may include an aluminumatom (Al). A content of the aluminum atom can be, for example, 0.5 to10.0 atom % with respect to 100 atom % of the iron atom. From aviewpoint of further preventing a decrease in reproducing output duringrepeated reproducing, the hexagonal strontium ferrite powder includesthe iron atom, the strontium atom, the oxygen atom, and the rare earthatom, and a content of the atoms other than these atoms is preferablyequal to or smaller than 10.0 atom %, more preferably 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one aspect, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting the content (unit: % by mass) of eachatom obtained by totally dissolving the hexagonal strontium ferritepowder by using the atomic weight. In addition, in the invention and thespecification, a given atom which is “not included” means that thecontent thereof obtained by performing total dissolving and measurementby using an ICP analysis device is 0% by mass. A detection limit of theICP analysis device is generally equal to or smaller than 0.01 ppm(parts per million) based on mass. The expression “not included” is usedas a meaning including that a given atom is included with the amountsmaller than the detection limit of the ICP analysis device. In oneaspect, the hexagonal strontium ferrite powder does not include abismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is to be understood to mean ferromagneticpowder from which an ε-iron oxide type crystal structure can be detectedas a main phase by X-ray diffraction analysis. For example, when thediffraction peak with the highest intensity in an X-ray diffractionspectrum obtained by X-ray diffraction analysis is assigned to theε-iron oxide type crystal structure, it shall be determined that theε-iron oxide type crystal structure is detected as a main phase. As amethod for producing ε-iron oxide powder, a method for producing ε-ironoxide powder from goethite and a reverse micelle method has been known.Both of the above-described production methods has been publicly known.Moreover, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp.S280-S284 and J. Mater. Chem. C, 2013, 1, pp. 5200-5206 can be referredto about a method for producing ε-iron oxide powder where some of Fe aresubstituted with substitutional atoms such as Ga, Co, Ti, Al, and Rh,for example. The method for producing ε-iron oxide powder which can beused as ferromagnetic powder in a magnetic layer of the magnetic tape,however, is not limited to these methods.

The activation volume of the ε-iron oxide powder is preferably 300 to1,500 nm³. The atomized ε-iron oxide powder showing the activationvolume in the range described above is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. The activation volume of the ε-iron oxide powder ispreferably equal to or greater than 300 nm³ and can also be, for exampleequal to or greater than 500 nm³. In addition, from a viewpoint offurther improving electromagnetic conversion characteristics, theactivation volume of the ε-iron oxide powder is more preferably equal toor smaller than 1,400 nm³, even more preferably equal to or smaller than1,300 nm³, still preferably equal to or smaller than 1,200 nm³, andstill more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic recording medium, it isdesirable that the mass magnetization σs of ferromagnetic powderincluded in the magnetic recording medium is high. In regards to thispoint, in one aspect, σs of the ε-iron oxide powder can be equal to orgreater than 8 A·m²/kg and can also be equal to or greater than 12A·m²/kg. On the other hand, from a viewpoint of noise reduction, σs ofthe ε-iron oxide powder is preferably equal to or smaller than 40A·m²/kg and more preferably equal to or smaller than 35 A·m²/kg.

In the invention and the specification, the “ferromagnetic powder” meansan aggregate of a plurality of ferromagnetic particles. The “aggregate”not only includes an aspect in which particles configuring the aggregatedirectly come into contact with each other, and also includes an aspectin which a binding agent or an additive is interposed between theparticles. The same applies to various powders such as non-magneticpowder in the invention and the specification. In the invention and thespecification, unless otherwise noted, average particle sizes of variouspowders such as the ferromagnetic powder are values measured by thefollowing method using a transmission electron microscope.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, the image is printed on printing paperor displayed on a display so that the total magnification ratio of500,000 to obtain an image of particles configuring the powder. A targetparticle is selected from the obtained image of particles, an outline ofthe particle is traced with a digitizer, and a size of the particle(primary particle) is measured. The primary particle is an independentparticle which is not aggregated.

The measurement described above is performed regarding 500 particlesrandomly extracted. An arithmetical mean of the particle size of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted.

As a method of collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted, (1) in acase where the shape of the particle observed in the particle imagedescribed above is a needle shape, a fusiform shape, or a columnar shape(here, a height is greater than a maximum long diameter of a bottomsurface), the size (particle size) of the particles configuring thepowder is shown as a length of a long axis configuring the particle,that is, a long axis length, (2) in a case where the shape of theparticle is a planar shape or a columnar shape (here, a thickness or aheight is smaller than a maximum long diameter of a plate surface or abottom surface), the particle size is shown as a maximum long diameterof the plate surface or the bottom surface, and (3) in a case where theshape of the particle is a sphere shape, a polyhedron shape, or anunspecified shape, and the long axis configuring the particles cannot bespecified from the shape, the particle size is shown as an equivalentcircle diameter. The equivalent circle diameter is a value obtained by acircle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetical mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, in a case of the definition (2), the average particle size is anaverage plate diameter. In a case of the definition (3), the averageparticle size is an average diameter (also referred to as an averageparticle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50 to 90 mass % and more preferably 60 to90 mass %. The components other than the ferromagnetic powder of themagnetic layer are at least a binding agent and fatty acid ester, andone or more kinds of additives may be randomly included. A high fillingpercentage of the ferromagnetic powder in the magnetic layer ispreferable from a viewpoint of improvement recording density.

Binding Agent

The magnetic tape is a coating type magnetic tape, and the magneticlayer includes a binding agent together with the ferromagnetic powder.As the binding agent, one or more kinds of resin is used. The resin maybe a homopolymer or a copolymer. As the binding agent, various resinsnormally used as a binding agent of the coating type magnetic recordingmedium can be used. For example, as the binding agent, a resin selectedfrom a polyurethane resin, a polyester resin, a polyamide resin, a vinylchloride resin, an acrylic resin obtained by copolymerizing styrene,acrylonitrile, or methyl methacrylate, a cellulose resin such asnitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylalresin such as polyvinyl acetal or polyvinyl butyral can be used alone ora plurality of resins can be mixed with each other to be used. Amongthese, a polyurethane resin, an acrylic resin, a cellulose resin, and avinyl chloride resin are preferable. These resins can be used as thebinding agent even in the non-magnetic layer and/or a back coating layerwhich will be described later. For the binding agent described above,description disclosed in paragraphs 0029 to 0031 of JP2010-024113A canbe referred to. In addition, the binding agent may be a radiationcurable resin such as an electron beam-curable resin. For the radiationcurable resin, descriptions disclosed in paragraphs 0044 and 0045 ofJP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent canbe, for example, 10,000 to 200,000 as a weight-average molecular weight.The weight-average molecular weight of the invention and thespecification is a value obtained by performing polystyrene conversionof a value measured by gel permeation chromatography (GPC). As themeasurement conditions, the following conditions can be used. Theweight-average molecular weight shown in examples which will bedescribed later is a value obtained by performing polystyrene conversionof a value measured under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In addition, a curing agent can also be used together with the bindingagent. As the curing agent, in one aspect, a thermosetting compoundwhich is a compound in which a curing reaction (crosslinking reaction)proceeds due to heating can be used, and in another aspect, aphotocurable compound in which a curing reaction (crosslinking reaction)proceeds due to light irradiation can be used. At least a part of thecuring agent is included in the magnetic layer in a state of beingreacted (crosslinked) with other components such as the binding agent,by proceeding the curing reaction in the manufacturing step of themagnetic tape. The preferred curing agent is a thermosetting compound,polyisocyanate is suitable. For details of the polyisocyanate,descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A canbe referred to, for example. The amount of the curing agent can be, forexample, 0 to 80.0 parts by mass with respect to 100.0 parts by mass ofthe binding agent in the magnetic layer forming composition, and ispreferably 50.0 to 80.0 parts by mass, from a viewpoint of improvementof strength of each layer such as the magnetic layer.

Fatty Acid Ester

The magnetic tape includes fatty acid ester in the magnetic layer. Thefatty acid ester may be included alone as one type or two or more typesthereof may be included. Examples of fatty acid ester include esters oflauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidicacid. Specific examples thereof include butyl myristate, butylpalmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate,sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyloleate, isocetyl stearate, isotridecyl stearate, octyl stearate,isooctyl stearate, amyl stearate, and butoxyethyl stearate.

The content of fatty acid ester, as the content of the magnetic layerforming composition, is, for example, 0.1 to 10.0 parts by mass and ispreferably 1.0 to 7.0 parts by mass with respect to 100.0 parts by massof ferromagnetic powder. In a case of using two or more kinds ofdifferent fatty acid esters as the fatty acid ester, the content thereofis the total content thereof. In the invention and the specification,the same applies to content of other components, unless otherwise noted.In addition, in the invention and the specification, a given componentmay be used alone or used in combination of two or more kinds thereof,unless otherwise noted.

In a case where the magnetic tape includes a non-magnetic layer betweenthe non-magnetic support and the magnetic layer, the content of fattyacid ester in a non-magnetic layer forming composition is, for example,0 to 15.0 parts by mass and is preferably 0.1 to 10.0 parts by mass,with respect to 100.0 parts by mass of non-magnetic powder.

Other Lubricants

The magnetic tape includes fatty acid ester which is one kind oflubricants at least in the magnetic layer. The lubricants other thanfatty acid ester may be randomly included in the magnetic layer and/orthe non-magnetic layer. As described above, the lubricant included inthe non-magnetic layer may be moved to the magnetic layer and present inthe surface of the magnetic layer. As the lubricant which may berandomly included, fatty acid can be used. In addition, fatty acid amideand the like can also be used. Fatty acid ester is known as a componentwhich can function as a fluid lubricant, whereas fatty acid and fattyacid amide are known as a component which can function as a boundarylubricant. It is considered that the boundary lubricant is a lubricantwhich can be adsorbed to a surface of powder (for example, ferromagneticpowder) and form a rigid lubricant film to decrease contact friction.

Examples of fatty acid include lauric acid, myristic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenicacid, erucic acid, and elaidic acid, and stearic acid, myristic acid,and palmitic acid are preferable, and stearic acid is more preferable.Fatty acid may be included in the magnetic layer in a state of salt suchas metal salt.

As fatty acid amide, amide of various fatty acid described above isused, and examples thereof include lauric acid amide, myristic acidamide, palmitic acid amide, and stearic acid amide.

Regarding fatty acid and a derivative of fatty acid (amide and ester), apart derived from fatty acid of the fatty acid derivative preferably hasa structure which is the same as or similar to that of fatty acid usedin combination. As an example, in a case of using stearic acid as fattyacid, it is preferable to use stearic acid ester and/or stearic acidamide.

The content of fatty acid in the magnetic layer forming composition is,for example, 0 to 10.0 parts by mass, preferably 0.1 to 10.0 parts bymass, and more preferably 1.0 to 7.0 parts by mass, with respect to100.0 parts by mass of the ferromagnetic powder. The content of fattyacid amide in the magnetic layer forming composition is, for example, 0to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, and morepreferably 0 to 1.0 part by mass with respect to 100.0 parts by mass ofthe ferromagnetic powder.

In a case where the magnetic tape includes a non-magnetic layer betweenthe non-magnetic support and the magnetic layer, the content of fattyacid in the non-magnetic layer forming composition is, for example, 0 to10.0 parts by mass, preferably 1.0 to 10.0 parts by mass, and morepreferably 1.0 to 7.0 parts by mass with respect to 100.0 parts by massof the non-magnetic powder. The content of fatty acid amide in thenon-magnetic layer forming composition is, for example, 0 to 3.0 partsby mass and preferably 0 to 1.0 part by mass with respect to 100.0 partsby mass of the non-magnetic powder.

Other Components

The magnetic layer may include one or more kinds of additives, ifnecessary, together with the various components described above. As theadditives, a commercially available product can be suitably selected andused according to the desired properties. Alternatively, a compoundsynthesized by a well-known method can be used as the additives. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include a non-magnetic filler, a dispersing agent, a dispersingassistant, an antibacterial agent, an antistatic agent, and anantioxidant. The non-magnetic filler is identical to the non-magneticpowder. As the non-magnetic filler, a non-magnetic filler (hereinafter,referred to as a “projection formation agent”) which can function as aprojection formation agent which forms projections suitably protrudedfrom the surface of the magnetic layer, and a non-magnetic filler(hereinafter, referred to as an “abrasive”) which can function as anabrasive can be used.

Non-Magnetic Filler

As the projection formation agent which is one aspect of thenon-magnetic filler, various non-magnetic powders normally used as aprojection formation agent can be used. These may be powder of aninorganic substance or powder of an organic substance. In one aspect,from a viewpoint of homogenization of friction properties, particle sizedistribution of the projection formation agent is not polydispersionhaving a plurality of peaks in the distribution and is preferablymonodisperse showing a single peak. From a viewpoint of availability ofmonodisperse particles, the projection formation agent is preferablypowder of inorganic substances (inorganic powder). Examples of theinorganic powder include powder of inorganic oxide such as metal oxide,metal carbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide, and powder of inorganic oxide is preferable. The projectionformation agent is more preferably colloidal particles and even morepreferably inorganic oxide colloidal particles. In addition, from aviewpoint of availability of monodisperse particles, the inorganic oxidecolloidal particles are more preferably colloidal silica (silicacolloidal particles). In the invention and the specification, the“colloidal particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, in a case where 1 g of theparticles is added to 100 mL of at least one organic solvent of at leastmethyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or amixed solvent including two or more kinds of the solvent described aboveat any mixing ratio. The average particle size of the colloidalparticles is a value obtained by a method disclosed in a paragraph 0015of JP2011-048878A as a measurement method of an average particlediameter. In addition, in another aspect, the projection formation agentis preferably carbon black.

An average particle size of the projection formation agent is, forexample, 30 to 300 nm and is preferably 40 to 200 nm.

The abrasive which is another aspect of the non-magnetic filler ispreferably non-magnetic powder having Mohs hardness exceeding 8 and morepreferably non-magnetic powder having Mohs hardness equal to or greaterthan 9. A maximum value of Mohs hardness is 10 of diamond. Specifically,powders of alumina (Al₂O₃), silicon carbide, boron carbide (B₄C), SiO₂,TiC, chromium oxide (Cr₂O₃), cerium oxide, zirconium oxide (ZrO₂), ironoxide, diamond, and the like can be used, and among these, aluminapowder such as α-alumina and silicon carbide powder are preferable. Inaddition, an average particle size of the abrasive is, for example, 30to 300 nm and is preferably 50 to 200 nm.

In addition, from a viewpoint that the projection formation agent andthe abrasive can exhibit the functions thereof in more excellent manner,the content of the projection formation agent of the magnetic layer ispreferably 1.0 to 4.0 parts by mass and more preferably 1.5 to 3.5 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.Meanwhile, the content of the abrasive in the magnetic layer ispreferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 partsby mass, and even more preferably 4.0 to 10.0 parts by mass with respectto 100.0 parts by mass of the ferromagnetic powder.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive of the magnetic layer formingcomposition. For the dispersing agent, a description disclosed inparagraphs 0061 and 0071 of JP2012-133837A can be referred to. Thedispersing agent may be included in the non-magnetic layer. For thedispersing agent which can be included in the non-magnetic layer, adescription disclosed in a paragraph 0061 of JP2012-133837A can bereferred to.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape maydirectly include a magnetic layer on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substances or powder of organic substances. In addition,carbon black and the like can be used. Examples of the inorganicsubstance include metal, metal oxide, metal carbonate, metal sulfate,metal nitride, metal carbide, and metal sulfide. These non-magneticpowders can be purchased as a commercially available product or can bemanufactured by a well-known method. For details thereof, descriptionsdisclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referredto. For carbon black which can be used in the non-magnetic layer,descriptions disclosed in paragraphs 0040 and 0041 of JP2010-024113A canbe referred to. The content (filling percentage) of the non-magneticpowder of the non-magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface provided with the magneticlayer. The back coating layer preferably includes one or both of carbonblack and inorganic powder. In regards to the binding agent included inthe back coating layer and various additives which can be randomlyincluded in the back coating layer, a well-known technology regardingthe back coating layer can be applied, and a well-known technologyregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied. For example, for the back coating layer,descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A andpage 4, line 65, to page 5, line 38, of U.S. Pat. No. 7,029,774B can bereferred to.

Various Thickness

A thickness of the non-magnetic support is preferably 3.0 to 6.0 μm.

A thickness of the magnetic layer is preferably equal to or smaller than0.15 μm and more preferably equal to or smaller than 0.1 from aviewpoint of realization of high-density recording required in recentyears. The thickness of the magnetic layer is even more preferably 0.01to 0.1 μm. The magnetic layer may be at least single layer, the magneticlayer may be separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is a totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and even more preferably 0.1 to 0.7 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scanning electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneportion of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of portions oftwo or more portions, for example, two portions which are randomlyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among those, from a viewpoint ofsolubility of the binding agent normally used in the coating typemagnetic recording medium, each layer forming composition preferablyincludes one or more ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of the solvent of each layerforming composition is not particularly limited, and can be set to bethe same as that of each layer forming composition of a typical coatingtype magnetic recording medium. In addition, steps of preparing eachlayer forming composition generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, if necessary. Each step may be divided into two or more stages.The component used in the preparation of each layer forming compositionmay be added at an initial stage or in a middle stage of each step. Inaddition, each raw material may be separately added in two or moresteps. For example, a binding agent may be separately added in akneading step, a dispersing step, and a mixing step for adjustingviscosity after the dispersion. In a manufacturing step of the magnetictape, a well-known manufacturing technology of the related art can beused in a part of the step or in the entire step. In the kneading step,an open kneader, a continuous kneader, a pressure kneader, or a kneaderhaving a strong kneading force such as an extruder is preferably used.The details of the kneading processes of these kneaders are disclosed inJP1989-106338A (JP-H01-106338A) and JP1989-079274A (JP-H01-079274A). Inaddition, in order to disperse each layer forming composition, glassbeads and/or other beads can be used. As such dispersion beads, zirconiabeads, titania beads, and steel beads which are dispersion beads havinghigh specific gravity are preferable. These dispersion beads arepreferably used by optimizing a bead diameter and a filling percentage.As a dispersing device, a well-known dispersing device can be used. Eachlayer forming composition may be filtered by a well-known method beforeperforming the coating step. The filtering can be performed by using afilter, for example. As the filter used in the filtering, a filterhaving a hole diameter of 0.01 to 3 μm (for example, filter made ofglass fiber or filter made of polypropylene) can be used, for example.

Coating Step

The magnetic layer can be formed, for example, by directly applying themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. In the aspect of performing the alignment process, while thecoating layer of the magnetic layer forming composition is wet, analignment process is performed with respect to the coating layer in analignment zone. For the alignment process, various well-knowntechnologies such as descriptions disclosed in a paragraph 0052 ofJP2010-024113A can be used. For example, the homeotropic alignmentprocess can be performed by a well-known method such as a method using apole opposing magnet. In the alignment zone, a drying speed of thecoating layer can be controlled depending on a temperature and an airflow of dry air and/or a transportation speed of the magnetic tape inthe alignment zone. In addition, the coating layer may be preliminarilydried before the transportation to the alignment zone.

The back coating layer can be formed by applying the back coating layerforming composition to a side of the non-magnetic support opposite to aside provided with the magnetic layer (or to be provided with themagnetic layer). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

For details of various other steps for manufacturing the magnetic tape,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to.

One Aspect of Preferred Manufacturing Method

As a preferred manufacturing method of the magnetic tape, amanufacturing method of applying vibration to the magnetic layer can beused, in order to improve uniformity of the thickness of the liquid filmof fatty acid ester on the surface of the magnetic layer. The inventorshave surmised that, by adding vibration, the liquid film of fatty acidester on the surface of the magnetic layer flows and the uniformity ofthe thickness of the liquid film is improved.

That is, the magnetic tape can be manufactured by a manufacturing methodof forming the magnetic layer by applying the magnetic layer formingcomposition including ferromagnetic powder, a binding agent, and fattyacid ester on the non-magnetic support and drying to form a magneticlayer, and applying vibration to the formed magnetic layer. Themanufacturing method is identical to the typical manufacturing method ofthe magnetic tape, except for applying vibration to the magnetic layer,and the details thereof are as described above.

Means for applying vibration are not particularly limited. For example,the vibration can be applied to the magnetic layer, by bringing thesurface of the non-magnetic support, provided with the magnetic layerformed, on a side opposite to the magnetic layer to come into contactwith a vibration imparting unit. The non-magnetic support, provided withthe magnetic layer formed, may run while coming into contact with avibration imparting unit. The vibration imparting unit, for example,includes an ultrasonic vibrator therein, and accordingly, vibration canbe applied to a product coming into contact with the unit. It ispossible to adjust the vibration applied to the magnetic layer by avibration frequency, and strength of the ultrasonic vibrator, and/or thecontact time with the vibration imparting unit. For example, the contacttime can be adjusted by a running speed of the non-magnetic support,provided with the magnetic layer formed, while coming into contact withthe vibration imparting unit. The vibration imparting conditions are notparticularly limited, and may be set so as to control the full width athalf maximum of the spacing distribution, particularly, the full widthat half maximum of the spacing distribution FWHM_(before) before vacuumheating. In order to set the vibration imparting conditions, apreliminary experiment can be performed before the actual manufacturing,and the conditions can be optimized.

In addition, the full width at half maximum of the spacing distributionFWHM_(after) after the vacuum heating tends to be decreased, in a casewhere the dispersion conditions of the magnetic layer formingcomposition are reinforced (for example, the number of times of thedispersion is increased, the dispersion time is extended, and the like),and/or the filtering conditions are reinforced (for example, a filterhaving a small hole diameter is used as a filter used in the filtering,the number of times of the filtering is increased, and the like). Theinventors have surmised that this is because the uniformity of theheight of the projection present on the surface of the magnetic layer isimproved, by improving dispersibility and/or the uniformity of theparticle size of the particulate matter included in the magnetic layerforming composition, particularly, the non-magnetic filler which mayfunction as the projection formation agent described above. Apreliminary experiment can be performed before the actual manufacturing,and the dispersion conditions and/or the filtering conditions can beoptimized.

In addition, in the magnetic tape including the magnetic layer includingcarbon black, it is effective to use the dispersing agent for improvingdispersibility of the carbon black as a magnetic layer component, inorder to decrease the full width at half maximum of the spacingdistribution FWHM_(after) after the vacuum heating. For example, organictertiary amine can be used as a dispersing agent of carbon black. Fordetails of the organic tertiary amine, descriptions disclosed inparagraphs 0011 to 0018 and 0021 of JP2013-049832A can be referred to.The organic tertiary amine is more preferably trialkylamine. An alkylgroup included in trialkylamine is preferably an alkyl group having 1 to18 carbon atoms. Three alkyl groups included in trialkylamine may be thesame as each other or different from each other. For details of thealkyl group, descriptions disclosed in paragraphs 0015 and 0016 ofJP2013-049832A can be referred to. As trialkylamine, trioctylamine isparticularly preferable.

As described above, it is possible to obtain a magnetic tape included inthe magnetic tape apparatus. However, the manufacturing method describedabove is merely an example, the FWHM_(before), the FWHM_(after), and thedifference (S_(after)−S_(before)) can be controlled to be in respectiveranges described above by any method capable of adjusting theFWHM_(before), the FWHM_(after), and the difference(S_(after)−S_(before)), and such an aspect is also included in theinvention.

A servo pattern can be formed on the magnetic layer of the magnetictape. The formation of a servo pattern on the magnetic layer isperformed by magnetizing a specific position of the magnetic layer witha servo pattern recording head (also referred to as a “servo writehead”). A shape of the servo pattern and disposition thereof in themagnetic layer for realizing the tracking are well known, and the regionmagnetized by the servo write head (position where a servo pattern isformed) is determined by standards. In regards to the servo pattern ofthe magnetic layer of the magnetic tape, a well-known technology can beused. For example, as a tracking system, a timing-based servo system andan amplitude-based servo system are known. The servo pattern which canbe formed on the magnetic layer of the magnetic tape may be a servopattern capable of allowing tracking of any system. In addition, a servopattern capable of allowing tracking in the timing-based servo systemand a servo pattern capable of allowing tracking in the amplitude-basedservo system may be formed on the magnetic layer.

In the magnetic tape, data is normally recorded on a data band of themagnetic tape. Accordingly, tracks are formed in the data band.Specifically, a plurality of regions including a servo pattern (referredto as “servo bands”) are generally present in the magnetic tape along alongitudinal direction. The data band is a region interposed between twoservo bands. For example, a track region 30 in FIG. 2 is a data band.The recording of data is performed on the data band, and a plurality oftracks are formed on the data band along the longitudinal direction. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 14 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 14, a servo frameSF on the servo band is configured with a servo sub-frame 1 (SSF1) and aservo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an Aburst (in FIG. 14, reference numeral A) and a B burst (in FIG. 14,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG.14, reference numeral C) and a D burst (in FIG. 14, reference numeralD). The C burst is configured with servo patterns C1 to C4 and the Dburst is configured with servo patterns D1 to D4. Such 18 servo patternsare disposed in the sub-frames in the arrangement of 5, 5, 4, 4, as thesets of 5 servo patterns and 4 servo patterns, and are used forrecognizing the servo frames. FIG. 14 shows one servo frame fordescription. However, in practice, in the magnetic layer of the magnetictape in which the tracking is performed in the timing-based servosystem, a plurality of servo frames are disposed in each servo band in arunning direction. In FIG. 14, an arrow shows the running direction. Forexample, an LTO Ultrium format tape generally includes 5,000 or moreservo frames per a tape length of 1 m, in each servo band of themagnetic layer. The servo element sequentially reads the servo patternsin the plurality of servo frames, while coming into contact with andsliding on the surface of the magnetic layer of the magnetic tapetransported in the magnetic tape apparatus.

In the timing-based servo system, for example, the servo patterns areconfigured of consecutive alignment of a plurality of pairs of magneticstripes (also referred to as “servo stripes”), in each pair of whichmagnetic stripes are not parallel with each other, in the longitudinaldirection of the magnetic tape. Servo signals can be obtained by readingthe servo stripes with the servo element.

In one aspect, information on the number of servo bands (also referredto as information on a “servo band identification (ID)” or a “uniquedata band identification method (UDIM)”) is embedded in each servo bandas shown in Japanese Patent Application Publication No. 2004-318983.This servo band ID is recorded shiftedly such that the position of aspecific pair of servo stripes, among a plurality of servo stripespresent in a servo band, should shift in the longitudinal direction ofthe magnetic tape. Specifically, the degree of shifting the specificpair of servo stripes among the plurality of pairs of servo stripes ischanged by each servo band. Accordingly, the recorded servo band ID isunique by each servo band, and the servo band is uniquely specified byreading one servo band with the servo signal reading element.

As another method for uniquely specifying a servo band, a method using astaggered technique as shown in ECMA (European Computer ManufacturersAssociation)-319 can be applied. In this staggered technique, a group ofa plurality of pairs of magnetic stripes (servo stripes), in each pairof which magnetic stripes are not parallel with each other and which areplaced consecutively in the longitudinal direction of the magnetic tape,are shiftedly recorded by each servo band in the longitudinal directionof the magnetic tape. A combination of ways of shifting for eachadjacent servo bands is unique in the entire magnetic tape. Accordingly,when a servo pattern is read with two servo signal reading elements, theservo band can be uniquely specified.

Information indicating a position in the longitudinal direction of themagnetic tape (also referred to as “longitudinal position (LPOS)information”) is also generally embedded in each servo band as shown inECMA-319. This LPOS information is also recorded by shifting theposition of the pair of servo stripes in the longitudinal direction ofthe magnetic tape. Unlike the UDIM information, the same signal isrecorded in each servo band in the case of LPOS information.

Other information different from UDIM information and LPOS informationas mentioned above can also be embedded in the servo band. In this case,the information to be embedded may be different by each servo band likethe UDIM information or may be the same by each servo band like the LPOSinformation.

As a method for embedding information in a servo band, a method otherthan the above-described method may also be employed. For example, amonga group of pairs of servo stripes, a predetermined pair of servo stripesis thinned out to record a predetermined code.

The servo write head has the same number of pairs of gaps correspondingto the respective pairs of servo patterns as the number of servo bands.Generally, a core and a coil are connected to each pair of gaps, and amagnetic field generated in the core by supplying a current pulse to thecoil can generate a leakage magnetic field to the pair of gaps. When aservo pattern is formed, a magnetic pattern corresponding to a pair ofgaps can be transferred to the magnetic tape by inputting a currentpulse while causing a magnetic tape to run over the servo write head, toform a servo pattern. Thus, the servo pattern can be formed. The widthof each gap can be set as appropriate according to the density of theservo pattern to be formed. The width of each gap can be set to, forexample, 1 μm or less, 1 to 10 μm, or 10 μm or larger.

Before forming a servo pattern on the magnetic tape, the magnetic tapeis generally subjected to a demagnetization (erasing) treatment. Thiserasing treatment may be performed by adding a uniform magnetic field tothe magnetic tape using a direct current magnet or an alternate currentmagnet. The erasing treatment includes direct current (DC) erasing andan alternating current (AC) erasing. The AC erasing is performed bygradually reducing the intensity of the magnetic field while invertingthe direction of the magnetic field applied to the magnetic tape. Incontrast, the DC erasing is performed by adding a one-direction magneticfield to the magnetic tape. The DC erasing further includes two methods.The first method is horizontal DC erasing of applying a one-directionmagnetic field along the longitudinal direction of the magnetic field.The second method is a vertical DC erasing of applying a one-directionmagnetic field along the thickness direction of the magnetic tape. Theerasing treatment may be applied to the entire magnetic tape of themagnetic tape, or may be applied to each servo band of the magnetictape.

The direction of the magnetic field of the servo pattern to be formed isdetermined according to the direction of the erasing. For example, whenthe magnetic tape has been subjected to the horizontal DC erasing, theservo pattern is formed so that the direction of the magnetic fieldbecomes reverse to the direction of the erasing. Accordingly, the outputof the servo signal, which can be yielded by reading the servo pattern,can be increased. As shown in Japanese Patent Application PublicationNo. 2012-53940, when a magnetic pattern is transferred to the magnetictape which has been subjected to the vertical DC erasing using the gaps,the servo signal, which has been yielded by reading the servo patternthus formed, has a unipolar pulse shape. In contrast, when a magneticpattern is transferred to the magnetic tape which has been subjected tothe parallel DC erasing, the servo signal, which has been yielded byreading the servo pattern thus formed, has a bipolar pulse shape.

The magnetic tape described above is generally accommodated in amagnetic tape cartridge and the magnetic tape cartridge is mounted inthe magnetic tape apparatus. The configuration of the magnetic tapecartridge is well known. For one aspect of the magnetic tape cartridge,the aforementioned description regarding the magnetic tape cartridge 12in FIG. 1 can be referred to.

According to one aspect, the following magnetic tape is also provided.

A magnetic tape comprising:

a non-magnetic support; and

a magnetic layer including a ferromagnetic powder, a binding agent, andfatty acid ester on the non-magnetic support,

in which a full width at half maximum of spacing distribution measuredby optical interferometry regarding a surface of the magnetic layerbefore performing a vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 15.0 nm,

a full width at half maximum of spacing distribution measured by opticalinterferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 15.0 nm, and

a difference (S_(after)−S_(before)) between a spacing S_(after) measuredby optical interferometry regarding the surface of the magnetic layerafter performing the vacuum heating with respect to the magnetic tapeand a spacing S_(before) measured by optical interferometry regardingthe surface of the magnetic layer before performing the vacuum heatingwith respect to the magnetic tape is greater than 0 nm and equal to orsmaller than 12.0 nm.

According to one aspect, the following magnetic tape is also provided.

A magnetic tape used for recording data or reading the recorded data,the magnetic tape comprising:

a non-magnetic support; and

a magnetic layer including a ferromagnetic powder, a binding agent, andfatty acid ester on the non-magnetic support,

in which a full width at half maximum of spacing distribution measuredby optical interferometry regarding a surface of the magnetic layerbefore performing a vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 15.0 nm,

a full width at half maximum of spacing distribution measured by opticalinterferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 15.0 nm, and

a difference (S_(after)−S_(before)) between a spacing Safer measured byoptical interferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape and aspacing S_(before) measured by optical interferometry regarding thesurface of the magnetic layer before performing the vacuum heating withrespect to the magnetic tape is greater than 0 nm and equal to orsmaller than 12.0 nm.

In one aspect, the reading of data may be performed by a reading elementunit.

In one aspect, the reading element unit may include a plurality ofreading elements each of which reads data by a linear scanning methodfrom a specific track region including a reading target track in a trackregion included in the magnetic tape.

In one aspect, a reading result for each reading element may beextracted by an extraction unit.

In one aspect, the extraction unit may extract data derived from thereading target track from the reading result for each reading element.

In one aspect, the extraction unit may perform a waveform equalizationprocess according to a deviation amount between positions of themagnetic tape and the reading element unit, with respect to each readingresult for each reading element, to extract data derived from thereading target track from the reading result.

For specific aspects of the magnetic tape, the reading element unit, andthe extraction unit, the aforementioned description can be referred to.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted. In addition, steps and evaluationsdescribed below are performed in an environment of an atmospheretemperature of 23° C.±1° C., unless otherwise noted.

Example 1

Magnetic Layer Forming Composition

Magnetic Liquid

-   -   Ferromagnetic powder (see Table 1): 100.0 parts    -   Sulfonate group-containing polyurethane resin: 15.0 parts    -   Cyclohexanone: 150.0 parts    -   Methyl ethyl ketone: 150.0 parts

Abrasive Solution

-   -   α-Alumina (Average particle size: 110 nm): 9.0 parts    -   A vinyl chloride copolymer (MR110 manufactured by Kaneka        Corporation): 0.7 parts    -   Cyclohexanone: 20.0 parts

Silica Sol

-   -   Colloidal silica (Average particle size: 120 nm): 3.5 parts    -   Methyl ethyl ketone: 8.2 parts

Other Components

-   -   Butyl stearate: 1.0 part    -   Stearic acid: 1.0 part    -   Polyisocyanate (CORONATE manufactured by Tosoh Corporation): 2.5        parts

Finishing Additive Solvent

-   -   Cyclohexanone: 180.0 parts    -   Methyl ethyl ketone: 180.0 parts

Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

-   -   (average particle size: 0.15 μm, average acicular ratio: 7,        Brunauer-Emmett-Teller (BET) specific surface area: 52 m²/g)

Carbon black (average particle size: 20 nm): 20.0 parts

An electron beam-curable vinyl chloride copolymer: 13.0 parts

An electron beam-curable polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: see Table 1

Stearic acid: see Table 1

Back Coating Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

-   -   (average particle size: 0.15 μm, average acicular ratio: 7, BET        specific surface area: 52 m²/g)

Carbon black (average particle size: 20 nm): 20.0 parts

Carbon black (average particle size: 100 nm): 3.0 parts

A vinyl chloride copolymer: 13.0 parts

Sulfonate group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Stearic acid: 3.0 parts

Polyisocyanate (CORONATE manufactured by Tosoh Corporation): 5.0 parts

Methyl ethyl ketone: 400.0 parts

Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

Various components of the magnetic liquid were kneaded by an openkneader and diluted, and subjected to a dispersion process of 12 passes,with a transverse beads mill dispersing device and zirconia (ZrO₂) beads(hereinafter, referred to as “Zr beads”) having a bead diameter of 0.5mm, by setting a bead filling percentage as 80 volume %, acircumferential speed of rotor distal end as 10 m/sec, and a retentiontime for 1 pass as 2 minutes, and the magnetic liquid was prepared.

The abrasive liquid was prepared by mixing and putting the variouscomponents described above to a vertical sand mill dispersing devicetogether with the Zr beads having a bead diameter of 1 mm, to performthe adjustment so that a value of bead volume/(abrasive liquidvolume+bead volume) was 60%, performing the sand mill dispersion processfor 180 minutes, extracting the liquid after the process, and performingan ultrasonic dispersion filtering process by using a flow typeultrasonic dispersion filtering device.

The magnetic liquid, the silica sol, the abrasive liquid, othercomponents, and the finishing additive solvent were introduced in adissolver stirrer, and stirred at a circumferential speed of 10 m/secfor 30 minutes. Then, a process at a flow rate of 7.5 kg/min wasperformed for the number of times of passes shown in Table 1 with a flowtype ultrasonic dispersing device, and then, the mixture was filteredfor the number of times shown in Table 1 with a filter having a holediameter shown in Table 1, to prepare a magnetic layer formingcomposition.

The non-magnetic layer forming composition was prepared by the followingmethod.

The components excluding lubricants (butyl stearate and stearic acid)were kneaded and diluted by an open kneader, and subjected to adispersion process with a transverse beads mill dispersing device. Afterthat, the lubricants (butyl stearate and stearic acid) were added,stirred, and mixed with a dissolver stirrer, to prepare a non-magneticlayer forming composition.

The back coating layer forming composition was prepared by the followingmethod.

The components excluding the lubricant (stearic acid), polyisocyanate,and methyl ethyl ketone (400.0 parts) were kneaded and diluted by anopen kneader, and subjected to a dispersion process with a transversebeads mill dispersing device. After that, the lubricant (stearic acid),polyisocyanate, and methyl ethyl ketone (400.0 parts) were added,stirred, and mixed with a dissolver stirrer, to prepare a back coatinglayer forming composition.

Manufacturing Magnetic Tape

The non-magnetic layer forming composition was applied onto apolyethylene naphthalate support having a thickness of 5.0 μm and driedso that the thickness after the drying becomes 1.0 μm, and then, anelectron beam was emitted with an energy of 40 kGy at an accelerationvoltage of 125 kV. The magnetic layer forming composition was appliedand dried so that the thickness after the drying becomes 0.1 μm to forma coating layer of the magnetic layer forming composition.

After that, the support, provided with the coating layer formed, wasinstalled in a vibration imparting device shown in FIG. 15 so that thesurface thereof on a side opposite to the surface where the coatinglayer is formed comes into contact with the vibration imparting unit,and the support (in FIG. 15, reference numeral 1), provided with thecoating layer formed, was transported at a transportation speed of 0.5m/sec, to apply vibration to the coating layer. In FIG. 15, a referencenumeral 2 denotes a guide roller (a reference numeral 2 denotes one oftwo guide rollers), a reference numeral 3 denotes the vibrationimparting device (vibration imparting unit including the ultrasonicvibrator), and an arrow denotes a transportation direction. The timefrom the start of the contact of random portion of the support, providedwith the coating layer formed, with the vibration imparting unit untilthe end of the contact is shown in Table 1 as the vibration impartingtime. The vibration imparting unit used includes an ultrasonic vibratortherein. The vibration was imparted by setting a vibration frequency andthe intensity of the ultrasonic vibrator as values shown in Table 1.

After that, the back coating layer forming composition was applied ontothe surface of the support on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, and dried so thatthe thickness after the drying becomes thickness of 0.5

After that, the surface smoothing treatment (calender process) wasperformed with a calender roll configured of only a metal roll, at acalender process speed of 80 m/min, linear pressure of 300 kg/cm (294kN/m), and a surface temperature of a calender roll of 110° C.

Then, the thermal treatment was performed in the environment of theatmosphere temperature of 70° C. for 36 hours. After the thermaltreatment, the slitting was performed so as to have a width of ½ inches(0.0127 meters), and the surface of the magnetic layer was cleaned witha tape cleaning device in which a nonwoven fabric and a razor blade areattached to a device including a sending and winding device of the slitso as to press the surface of the magnetic layer.

By doing so, a magnetic tape was manufactured.

In a state where the magnetic layer of the manufactured magnetic tapewas demagnetized, servo patterns having disposition and shapes accordingto the LTO Ultrium format were formed on the magnetic layer by using aservo write head. Accordingly, a magnetic tape including data bands,servo bands, and guide bands in the disposition according to the LTOUltrium format in the magnetic layer, and including servo patternshaving the disposition and the shape according to the LTO Ultrium formaton the servo band is manufactured.

Examples 2 to 15 and Comparative Examples 1 to 19

A magnetic tape was obtained in the same manner as in Example 1, exceptthat various items shown in Table 1 were changed as shown in Table 1.

In Table 1, in the comparative examples in which “none” is disclosed ina column of the ultrasonic vibration imparting conditions, a magnetictape was manufactured by a manufacturing step in which the vibrationimparting is not performed.

In Table 1, “BaFe” shown in a column of the ferromagnetic powder of themagnetic layer indicates hexagonal barium ferrite powder (averageparticle size: 25 nm).

In Table 1, “SrFe” indicates hexagonal strontium ferrite powder (averageparticle size: 18 nm) prepared by the method disclosed in Example 14 ofJP2015-127985A.

In Table 1, “ε-iron oxide” indicates ε-iron oxide powder (averageparticle size: 13 nm) prepared by the following method.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 6.3 g of iron (III) nitratenonahydrate, 5.0 g of gallium (III) nitrate octahydrate, 1.5 g ofpolyvinyl pyrrolidone (PVP) in 90 g of pure water, while stirring byusing a magnetic stirrer, in an atmosphere under the conditions of anatmosphere temperature of 25° C., and the mixture was stirred for 2hours still under the temperature condition of the atmospheretemperature of 25° C. A citric acid solution obtained by dissolving 1 gof citric acid in 9 g of pure water was added to the obtained solutionand stirred for 1 hour. The powder precipitated after the stirring wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1030° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to thermal treatment for 4 hours.

The thermal-treated precursor of ferromagnetic powder was put intosodium hydroxide (NaOH) aqueous solution having a concentration of 4mol/L, the liquid temperature was held at 70° C., stirring was performedfor 24 hours, and accordingly, a silicon acid compound which was animpurity was removed from the thermal-treated precursor of ferromagneticpowder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the powder X-ray diffraction (XRD) was performed, and it was confirmedthat the obtained ferromagnetic powder has a crystal structure of asingle phase which is an ε phase not including a crystal structure of anα phase and a γ phase from the peak of the XRD pattern.

Evaluation of Physical Properties

(1) Full Width at Half Maximum of Spacing Distributions FWHM_(before)and FWHM_(after) Before and after Vacuum Heating

The full width at half maximum of the spacing distributionsFWHM_(before) and FWHM_(after) before and after vacuum heating,regarding each magnetic tape of the examples and the comparativeexamples, were acquired by the following method by using a tape spacinganalyzer (TSA) (manufactured by Micro Physics, Inc.).

In a state where a glass sheet included in the TSA was disposed on thesurface of the magnetic layer of the magnetic tape, a hemisphere waspressed against the surface of the back coating layer of the magnetictape at a pressure of 5.05×10⁴ N/m (0.5 atm) by using a hemisphere madeof urethane included in the TSA as a pressing member. In this state, agiven region (150,000 to 200,000 μm²) of the surface of the magneticlayer of the magnetic tape was irradiated with white light from astroboscope included in the TSA through the glass sheet, and theobtained reflected light was received by a charge-coupled device (CCD)through an interference filter (filter selectively passing light at awavelength of 633 nm), and thus, an interference fringe image generatedon the uneven part of the region was obtained.

This image was divided into 300,000 points, a distance (spacing) betweenthe surface of the glass sheet at each point on the magnetic tape sideand the surface of the magnetic layer of the magnetic tape was acquired,and the full width at half maximum of spacing distribution was fullwidth at half maximum, in a case where this spacing was shown with ahistogram, and this histogram was fit with Gaussian distribution.

The vacuum heating was performed by storing the magnetic tape in avacuum constant temperature drying machine with a degree of vacuum of200 Pa to 0.01 Mpa and at inner atmosphere temperature of 70° C. to 90°C. for 24 hours.

(2) Difference (S_(after)−S_(before))

The difference (S_(after)−S_(before)) was a value obtained bysubtracting a mode of the histogram before the vacuum heating from amode of the histogram after the vacuum heating obtained in the section(1).

Evaluation of Performance

(1) The recording of data was performed on the magnetic layer of eachmagnetic tape of the examples and the comparative examples by using arecording and reproducing head mounted on TS1155 tape drive manufacturedby IBM, under recording conditions of a rate of 6 m/s, a linearrecording density of 600 kbpi (255 bit PRBS), and a track pitch of 2 μm.The unit kbpi is a unit of linear recording density (cannot be convertedinto SI unit system). The PRBS is an abbreviation of Pseudo Random BitSequence.

By the recording, a specific track region, where the reading targettrack is positioned, is formed on the magnetic layer of each magnetictape between two adjacent tracks, that is, between a first noise mixingsource track and a second noise mixing source track.

(2) The following data reading was performed as a model experiment ofperforming the data reading using the reading element unit including tworeading elements disposed in adjacent state. In the following modelexperiment, the data reading was performed by bringing the surface ofthe magnetic layer and the reading element into contact with each otherto slide on each other.

The reading was started in a state where the magnetic head including asingle reading element was disposed so that the center of the readingtarget track in the tape width direction coincides with the center ofthe reading element in the track width direction, and a first datareading was performed. During this first data reading, the servo patternwas read by the servo element, and the tracking in the timing-basedservo system was also performed. In addition, the data reading operationwas performed by the reading element synchronously with the servopattern reading operation.

Then, the position of the same magnetic head was deviated in the tapewidth direction (one adjacent track side) by 500 nm, and a second datareading was performed, in the same manner as in the first data reading.The two times of data reading described above were respectivelyperformed under reading conditions of a reproducing element width of 0.2μm, a rate of 4 m/s, and a sampling rate:bit rate of 1.25 times.

A reading signal obtained by the first data reading was input to anequalizer, and the waveform equalization process according to thedeviation amount of the positions between the magnetic tape and themagnetic head (reading element) of the first data reading was performed.This waveform equalization process is a process performed as follows. Aratio between an overlapping region of the reading element and thereading target track and an overlapping region of the reading elementand the adjacent track is specified from the deviation amount of theposition obtained by reading the servo pattern formed at regular cycleby the servo element. A convolution arithmetic operation of a tapcoefficient derived from this specific ratio using an arithmeticexpression, was performed with respect to the reading signal, andaccordingly, the waveform equalization process was performed. Thearithmetic expression is an arithmetic expression in which ExtendedPartial Response class 4 (EPR4) is set as a reference waveform (target).Regarding a reading signal obtained in the second data reading, thewaveform equalization process was performed in the same manner.

By performing a phase matching process of the two reading signalssubjected to the waveform equalization process (hereinafter, referred toas “two-dimensional signal process”), a reading signal which wasexpected to be obtained by the reading element unit including tworeading elements disposed in an adjacent state (reading elementpitch=500 nm) was obtained. Regarding the reading signal obtained bydoing so, an SNR at a signal detection point was calculated.

(3) The operation of (2) was repeated while performing track off-set ofthe position of the reading element at the start of the first datareading to the first noise mixing source track and the second noisemixing source track, respectively from the center of the reading targettrack in the tape width direction at interval of 0.1 μm, and an envelopeof the SNR with respect to the track position was obtained.

In Table 1, in the examples and the comparative examples in which“performed” is disclosed in a column of the “two-dimensional signalprocess”, the envelope of the SNR was obtained by the method describedabove.

In Table 1, in the comparative examples in which “none” is disclosed ina column of the “two-dimensional signal process”, the second datareading was not performed, and the envelope of the SNR was obtainedregarding the first data reading result (that is, data reading resultobtained with only a single element).

(4) The envelope of the SNR of Comparative Example 1 was set as areference envelope, and the SNR decreased from the SNR of the trackcenter of the reference envelope by −3 dB was set as an SNR lower limitvalue. Regarding each envelope, the maximum track off-set amount equalto or greater than the lower limit value was set as allowable trackoff-set amount. In respective examples and the comparative examples, arate of increase of the allowable track off-set amount with respect tothe allowable track off-set amount of Comparative Example 1 was obtainedas a “rate of increase of the allowable track off-set amount”.

The results described above are shown in Table 1 (Tables 1-1 to 1-7).

TABLE 1-1 Unit Example 1 Example 2 Example 3 Example 4 Example 5Magnetic layer Ferromagnetic Kind — BaFe BaFe BaFe BaFe BaFe powderNon-magnetic Butyl stearate Content Part 4.0 4.0 4.0 2.0 15.0 layerforming Stearic acid Content Part 1.0 1.0 1.0 1.0 1.0 compositionPreparation Ultrasonic Imparting time Second 0.5 3.0 5.0 0.5 0.5condition vibration imparting Frequency kHz 30 30 30 30 30 conditionsIntensity W 100 100 100 100 100 Magnetic layer Number of times of passesof flow type Times 2 30 30 2 2 forming ultrasonic dispersing devicecomposition Number of times of filtering Times 1 5 5 1 1 preparationFilter hole diameter μm 1.0 0.5 0.5 1.0 1.0 conditions PhysicalS_(after)-S_(before) nm 3.2 3.2 3.2 1.5 11.0 properties FWHM_(before) nm13.0 7.0 3.7 13.1 13.0 FWHM_(after) nm 12.9 7.2 3.8 12.9 12.9Two-dimensional signal process — Performed Performed Performed PerformedPerformed Performance Rate of increase of allowable track off-set amount% 22 28 32 23 22

TABLE 1-2 Unit Example 6 Example 7 Example 8 Example 9 Example 10Magnetic layer Ferromagnetic Kind — SrFe SrFe SrFe SrFe SrFe powderNon-magnetic layer Butyl stearate Content Part 4.0 4.0 4.0 2.0 15.0forming composition Stearic acid Content Part 1.0 1.0 1.0 1.0 1.0Preparation condition Ultrasonic vibration Imparting time Second 0.5 3.05.0 0.5 0.5 imparting Frequency kHz 30 30 30 30 30 conditions IntensityW 100 100 100 100 100 Magnetic layer Number of Times 2 30 30 2 2 formingtimes of passes composition of flow type preparation ultrasonicconditions dispersing device Number of Times 1 5 5 1 1 times offiltering Filter hole μm 1.0 0.5 0.5 1.0 1.0 diameter Physicalproperties S_(after)-S_(before) nm 3.2 3.1 3.1 1.4 11.2 FWHM_(before) nm13.1 6.9 3.8 13.1 13.0 FWHM_(after) nm 12.9 7.2 3.7 13.0 12.9Two-dimensional signal process — Performed Performed Performed PerformedPerformed Performance Rate of increase of allowable track % 24 30 35 2223 off-set amount

TABLE 1-3 Unit Example 11 Example 12 Example 13 Example 14 Example 15Magnetic layer Ferromagnetic Kind — ε-Iron oxide ε-Iron oxide ε-Ironoxide ε-Iron oxide ε-Iron oxide powder Non-magnetic layer Butyl stearateContent Part 4.0 4.0 4.0 2.0 15.0 forming composition Stearic acidContent Part 1.0 1.0 1.0 1.0 1.0 Preparation condition UltrasonicImparting time Second 0.5 3.0 5.0 0.5 0.5 vibration Frequency kHz 30 3030 30 30 imparting Intensity W 100 100 100 100 100 conditions Magneticlayer Number of Times 2 30 30 2 2 forming times of passes composition offlow type preparation ultrasonic conditions dispersing device Number ofTimes 1 5 5 1 1 times of filtering Filter hole μm 1.0 0.5 0.5 1.0 1.0diameter Physical properties S_(after)-S_(before) nm 3.1 3.2 3.2 1.611.2 FWHM_(before) nm 13.0 7.0 3.9 12.9 13.1 FWHM_(after) nm 12.9 7.13.8 12.9 12.9 Two-dimensional signal process — Performed PerformedPerformed Performed Performed Performance Rate of increase of allowable% 26 32 37 22 21 track off-set amount

TABLE 1-4 Comparative Comparative Comparative Comparative ComparativeUnit Example 1 Example 2 Example 3 Example 4 Example 5 Magnetic layerFerromagnetic Kind — BaFe BaFe BaFe BaFe BaFe powder Non-magnetic Butylstearate Content Part 4.0 15.0 4.0 19.0 0.0 layer forming Stearic acidContent Part 1.0 1.0 1.0 1.0 1.0 composition Preparation UltrasonicImparting time Second None None 0.5 0.5 0.5 condition vibrationimparting Frequency kHz 30 30 30 conditions Intensity W 100 100 100Magnetic layer Number of Times 2 2 1 2 2 forming times of compositionpasses of flow preparation type ultrasonic conditions dispersing deviceNumber of Times 1 1 1 1 1 times of filtering Filter hole μm 1.0 1.0 1.01.0 1.0 diameter Physical S_(after)-S_(before) nm 3.1 11.0 3.1 14.0 0properties FWHM_(before) nm 18.2 18.1 13.0 13.0 12.9 FWHM_(after) nm12.8 12.9 17.9 13.0 13.0 Two-dimensional signal process — None None NoneNone None Performance Rate of increase of allowable % 0 0 0 −3 −4 trackoff-set amount

TABLE 1-5 Comparative Comparative Comparative Comparative ComparativeUnit Example 6 Example 7 Example 8 Example 9 Example 10 Magnetic layerFerromagnetic Kind — BaFe BaFe BaFe BaFe BaFe powder Non-magnetic Butylstearate Content Part 4.0 4.0 4.0 19.0 0.0 layer forming Stearic acidContent Part 2.0 1.0 1.0 1.0 1.0 composition Preparation UltrasonicImparting time Second None None 0.5 0.5 0.5 condition vibrationimparting Frequency kHz 30 30 30 conditions Intensity W 100 100 100Magnetic layer Number of Times 2 2 1 2 2 forming times of passescomposition of flow type preparation ultrasonic conditions dispersingdevice Number of Times 1 1 1 1 1 times of filtering Filter hole μm 1.01.0 1.0 1.0 1.0 diameter Physical S_(after)-S_(before) nm 3.2 3.2 3.114.0 0 properties FWHM_(before) nm 18.0 18.3 13.2 13.2 13.1 FWHM_(after)nm 12.9 12.8 18.0 12.9 12.9 Two-dimensional signal process — NonePerformed Performed Performed Performed Performance Rate of increase ofallowable track % 0 14 14 11 10 off-set amount

TABLE 1-6 Comparative Comparative Comparative Comparative ComparativeComparative Unit Example 11 Example 12 Example 13 Example 14 Example 15Example 16 Magnetic Ferromagnetic Kind — BaFe BaFe BaFe SrFe SrFe SrFelayer powder Non- Butyl stearate Content Part 4.0 4.0 4.0 4.0 4.0 4.0magnetic Stearic acid Content Part 2.0 1.0 1.0 1.0 1.0 1.0 layer formingcomposition Preparation Ultrasonic Imparting Second None 0.5 3.0 NoneNone 0.5 condition vibration time kHz 30 30 30 imparting Frequency W 100100 100 conditions Intensity Magnetic layer Number of Times 2 2 30 2 2 2forming times of composition passes of preparation flow type conditionsultrasonic dispersing device Number of Times 1 1 5 1 1 1 times offiltering Filter hole μm 1.0 1.0 0.5 1.0 1.0 1.0 diameter PhysicalS_(after)-S_(before) nm 3.1 3.2 3.2 3.0 3.1 3.1 properties FWHM_(before)nm 18.2 13.2 7.0 18.1 18.1 13.1 FWHM_(after) nm 12.8 12.8 7.0 12.8 12.912.8 Two-dimensional signal process — Performed None None None PerformedNone Performance Rate of increase of % 14 4 6 2 16 6 allowable trackoff-set amount

TABLE 1-7 Comparative Comparative Unit Example 17 Example 18 ComparativeExample 19 Magnetic layer Ferromagnetic Kind — ε-Iron oxide ε-Iron oxideε-Iron oxide powder Non-magnetic layer Butyl stearate Content Part 4.04.0 4.0 forming composition Stearic acid Content Part 1.0 1.0 1.0Preparation condition Ultrasonic vibration Imparting time Second NoneNone 0.5 imparting conditions Frequency kHz 30 Intensity W 100 Magneticlayer Number of times of Times 2 2 2 forming passes of flow typecomposition ultrasonic dispersing preparation device conditions Numberof times of Times 1 1 1 filtering Filter hole diameter μm 1.0 1.0 1.0Physical properties S_(after)-S_(before) nm 3.1 3.0 3.0 FWHM_(before) nm18.1 18.2 13.1 FWHM_(after) nm 12.9 13.0 12.9 Two-dimensional signalprocess — None Performed None Performance Rate of increase of allowabletrack off-set % 4 18 8 amount

As shown in Table 1, according to the examples, the rate of increase ofthe allowable track off-set amount equal to or greater than 20% could berealized.

A large allowable track off-set amount obtained by the method describedabove is advantageous, from a viewpoint of performing the reproducingwith high reproducing quality, even with a small track margin. From thisviewpoint, the rate of increase of the allowable track off-set amount ispreferably equal to or greater than 20%.

One aspect of the invention is effective for usage of magnetic recordingfor which reproducing of data recorded with high density with highreproducing quality is desired.

What is claimed is:
 1. A magnetic tape apparatus comprising: a magnetictape; a reading element unit; and an extraction unit, wherein themagnetic tape includes a non-magnetic support, and a magnetic layerincluding a ferromagnetic powder, a binding agent, and fatty acid esteron the non-magnetic support, a full width at half maximum of spacingdistribution measured by optical interferometry regarding a surface ofthe magnetic layer before performing a vacuum heating with respect tothe magnetic tape is greater than 0 nm and equal to or smaller than 15.0nm, a full width at half maximum of spacing distribution measured byoptical interferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 15.0 nm, a differenceS_(after)−S_(before) between a spacing S_(after) measured by opticalinterferometry regarding the surface of the magnetic layer afterperforming the vacuum heating with respect to the magnetic tape and aspacing S_(before) measured by optical interferometry regarding thesurface of the magnetic layer before performing the vacuum heating withrespect to the magnetic tape is greater than 0 nm and equal to orsmaller than 12.0 nm, the reading element unit includes a plurality ofreading elements each of which reads data by a linear scanning methodfrom a specific track region including a reading target track in a trackregion included in the magnetic tape, and the extraction unit performs awaveform equalization process according to a deviation amount betweenpositions of the magnetic tape and the reading element unit, withrespect to each reading result for each reading element, to extract dataderived from the reading target track from the reading result.
 2. Themagnetic tape apparatus according to claim 1, wherein parts of theplurality of reading elements are overlapped each other in a runningdirection of the magnetic tape.
 3. The magnetic tape apparatus accordingto claim 2, wherein the specific track region is a region including thereading target track and adjacent tracks which are adjacent to thereading target track, and each of the plurality of reading elementsstraddles over both of the reading target track and the adjacent track,in a case where a positional relationship with the magnetic tape ischanged.
 4. The magnetic tape apparatus according to claim 1, whereinthe plurality of reading elements are disposed in a line in a state ofbeing adjacent to each other, in a width direction of the magnetic tape.5. The magnetic tape apparatus according to claim 1, wherein theplurality of reading elements fall in the reading target track in awidth direction of the magnetic tape.
 6. The magnetic tape apparatusaccording to claim 1, wherein the waveform equalization process isperformed by using a tap coefficient determined in accordance with thedeviation amount.
 7. The magnetic tape apparatus according to claim 6,wherein, regarding each of the plurality of reading elements, a ratiobetween an overlapping region with the reading target track and anoverlapping region with an adjacent track which is adjacent to thereading target track is specified from the deviation amount, and the tapcoefficient is determined in accordance with the specified ratio.
 8. Themagnetic tape apparatus according to claim 2, wherein the waveformequalization process is performed by using a tap coefficient determinedin accordance with the deviation amount.
 9. The magnetic tape apparatusaccording to claim 8, wherein, regarding each of the plurality ofreading elements, a ratio between an overlapping region with the readingtarget track and an overlapping region with an adjacent track which isadjacent to the reading target track is specified from the deviationamount, and the tap coefficient is determined in accordance with thespecified ratio.
 10. The magnetic tape apparatus according to claim 3,wherein the waveform equalization process is performed by using a tapcoefficient determined in accordance with the deviation amount.
 11. Themagnetic tape apparatus according to claim 10, wherein, regarding eachof the plurality of reading elements, a ratio between an overlappingregion with the reading target track and an overlapping region with anadjacent track which is adjacent to the reading target track isspecified from the deviation amount, and the tap coefficient isdetermined in accordance with the specified ratio.
 12. The magnetic tapeapparatus according to claim 4, wherein the waveform equalizationprocess is performed by using a tap coefficient determined in accordancewith the deviation amount.
 13. The magnetic tape apparatus according toclaim 12, wherein, regarding each of the plurality of reading elements,a ratio between an overlapping region with the reading target track andan overlapping region with an adjacent track which is adjacent to thereading target track is specified from the deviation amount, and the tapcoefficient is determined in accordance with the specified ratio. 14.The magnetic tape apparatus according to claim 1, wherein the deviationamount is determined in accordance with a result obtained by reading aservo pattern applied to the magnetic tape in advance, by a servoelement.
 15. The magnetic tape apparatus according to claim 14, whereina reading operation by the reading element unit is performedsynchronously with a reading operation by the servo element.
 16. Themagnetic tape apparatus according to claim 1, wherein the extractionunit includes a two-dimensional FIR filter, and the two-dimensional FIRfilter composes each result obtained by performing the waveformequalization process with respect to each reading result for eachreading element, to extract data derived from the reading target trackfrom the reading result.
 17. The magnetic tape apparatus according toclaim 1, wherein the plurality of reading elements are a pair of readingelements.
 18. The magnetic tape apparatus according to claim 1, whereinthe full width at half maximum of spacing distribution measured byoptical interferometry regarding the surface of the magnetic layerbefore performing the vacuum heating with respect to the magnetic tapeis 2.0 nm to 15.0 nm.
 19. The magnetic tape apparatus according to claim1, wherein the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the magneticlayer after performing the vacuum heating with respect to the magnetictape is 2.0 nm to 15.0 nm.
 20. The magnetic tape apparatus according toclaim 1, wherein the difference S_(after)−S_(before) is 1.0 nm to 12.0nm.